From 02c7e41ef86becc84f2eca2e8e90726eb684eefe Mon Sep 17 00:00:00 2001
From: "russell@unturf.com" <russell@unturf.com>
Date: Thu, 7 May 2026 17:58:50 -0400
Subject: [PATCH] loss_report: land ticket #000022 (adapter LossReport sidecar)
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

Typed loss ledger for adapter / canonicalizer drops, transforms, and
normalizations. Sidecar — never enters cache_key, document_root,
run_dag_root, or audit_events. Loss policy lives in its own
loss_report_policy_hash so toggling reporting does NOT invalidate
prior QA cache entries (corrected pre-land per GPT-5.5 review).

- adapter_loss_reports table: PK (chunk_id, stage, canonicalization_version,
  loss_kind); columns include loss_mode {pure_drop|transform|quarantine|
  normalize}, bytes_dropped, occurrence_count, input/output_length_bytes,
  sample_excerpt, sample_hash, adapter_name/version, loss_report_policy_hash
- arborist/sources/loss_report.py: LossEvent, LossCollector with
  add()/record_delta()/set_lengths()/events(), record_losses() batched
  idempotent insert, compute_loss_report_policy_hash() pure function
- wikitext.to_base() emits ref_tag, self_closing_ref_tag, file_link,
  image_link, category_link, strip_code_transform, whitespace_run.
  loss_collector=None default keeps verifier/runner/query path unchanged
- html_page parse_html / _normalize_text emit script_block, style_block,
  html_chrome, whitespace_run; HtmlPageSource gains loss_report_*
  __init__ flags. Document-scope events anchor to first chunk_id at
  ingest via Document.extra['loss_events']
- ingest.ingest_source: per-chunk to_base() with collector for
  wikipedia_* sources; persisted via record_losses inside the same
  transaction as chunk inserts. Default loss_report_enabled=True
- arborist losses CLI subcommand: --document-root / --chunk-id /
  --kind / --stage / --summary / --json. arborist ingest gains
  --no-loss-report / --no-loss-excerpts / --loss-excerpt-bytes
- tests/test_loss_report.py: 15 tests covering bit-identical
  regression, loss-kind taxonomy, byte-conservation property test
  (loss-mode-aware), idempotent persistence, document_root invariant
  under toggle, policy hash purity

1091 tests pass, 0 audit-chain breaks across all 7 shards.
---
 arborist/cli.py                               | 158 +++++++
 arborist/ingest.py                            |  92 +++-
 arborist/sources/html_page.py                 | 109 ++++-
 arborist/sources/loss_report.py               | 329 ++++++++++++++
 arborist/store.py                             | 107 +++++
 arborist/wikitext.py                          |  84 +++-
 docs/TICKETS.md                               |   2 +-
 .../ticket-000022-adapter-loss-report.md      | 211 +++++++--
 tests/test_loss_report.py                     | 417 ++++++++++++++++++
 9 files changed, 1460 insertions(+), 49 deletions(-)
 create mode 100644 arborist/sources/loss_report.py
 create mode 100644 tests/test_loss_report.py

diff --git a/arborist/cli.py b/arborist/cli.py
index fef6a78..164bb26 100644
--- a/arborist/cli.py
+++ b/arborist/cli.py
@@ -164,6 +164,9 @@ def _cmd_ingest(args: argparse.Namespace) -> int:
             batch_size=args.batch_size,
             resume=args.resume,
             progress=progress,
+            loss_report_enabled=not args.no_loss_report,
+            loss_report_excerpts=not args.no_loss_excerpts,
+            loss_report_max_excerpt_bytes=args.loss_excerpt_bytes,
         )
     finally:
         conn.close()
@@ -1150,6 +1153,98 @@ def _short(s: str, n: int) -> str:
     return s if len(s) <= n else s[: n - 3] + "..."
 
 
+def _cmd_losses(args: argparse.Namespace) -> int:
+    """Sidecar diagnostic: list adapter_loss_reports rows.
+
+    Read-only. Filters: --document-root, --chunk-id, --kind, --stage.
+    With --summary, aggregates per (stage, loss_kind) for a single
+    document. See ticket #000022 §3.6.
+    """
+    conn = (
+        connect_query(args.db, shards_dir=args.global_shards_dir)
+        if args.global_shards_dir
+        else connect(args.db)
+    )
+    try:
+        where: list[str] = []
+        params: list = []
+        if args.document_root:
+            where.append("document_root = ?")
+            params.append(args.document_root)
+        if args.chunk_id is not None:
+            where.append("chunk_id = ?")
+            params.append(args.chunk_id)
+        if args.kind:
+            where.append("loss_kind = ?")
+            params.append(args.kind)
+        if args.stage:
+            where.append("stage = ?")
+            params.append(args.stage)
+        clause = (" WHERE " + " AND ".join(where)) if where else ""
+
+        if args.summary:
+            sql = (
+                "SELECT stage, loss_kind, loss_mode, "
+                "       SUM(bytes_dropped) AS total_bytes, "
+                "       SUM(occurrence_count) AS total_occ, "
+                "       COUNT(*) AS row_count "
+                "FROM adapter_loss_reports"
+                + clause +
+                " GROUP BY stage, loss_kind, loss_mode "
+                "ORDER BY stage, total_bytes DESC"
+            )
+            rows = conn.execute(sql, params).fetchall()
+            if args.json:
+                out = [dict(r) for r in rows]
+                print(json.dumps(out, indent=2, ensure_ascii=False))
+            else:
+                if not rows:
+                    print("(no loss rows match)")
+                    return 0
+                print(f"{'stage':<18} {'kind':<28} {'mode':<11} {'occ':>7} {'bytes':>10} {'rows':>6}")
+                for r in rows:
+                    print(
+                        f"{r['stage']:<18} {r['loss_kind']:<28} "
+                        f"{r['loss_mode']:<11} {r['total_occ']:>7,} "
+                        f"{r['total_bytes']:>10,} {r['row_count']:>6,}"
+                    )
+            return 0
+
+        sql = (
+            "SELECT chunk_id, document_root, stage, canonicalization_version, "
+            "       loss_kind, loss_mode, bytes_dropped, occurrence_count, "
+            "       input_length_bytes, output_length_bytes, sample_excerpt, "
+            "       sample_hash, adapter_name, adapter_version, "
+            "       loss_report_policy_hash, created_at "
+            "FROM adapter_loss_reports"
+            + clause +
+            " ORDER BY chunk_id, stage, loss_kind LIMIT ?"
+        )
+        params.append(args.limit)
+        rows = conn.execute(sql, params).fetchall()
+        if args.json:
+            out = [dict(r) for r in rows]
+            print(json.dumps(out, indent=2, ensure_ascii=False))
+            return 0
+        if not rows:
+            print("(no loss rows match)")
+            return 0
+        for r in rows:
+            print(
+                f"chunk={r['chunk_id']} doc={r['document_root'][:12]}.. "
+                f"stage={r['stage']} kind={r['loss_kind']} "
+                f"mode={r['loss_mode']} occ={r['occurrence_count']} "
+                f"bytes={r['bytes_dropped']}"
+            )
+            if r["sample_excerpt"]:
+                print(f"  excerpt: {_short(r['sample_excerpt'], 120)!r}")
+            elif r["sample_hash"]:
+                print(f"  sample_hash: {r['sample_hash'][:16]}..")
+        return 0
+    finally:
+        conn.close()
+
+
 def _falsify_cache_key(
     cache_key_value: str,
     *,
@@ -3677,6 +3772,32 @@ def build_parser() -> argparse.ArgumentParser:
             "+ ETA in progress output"
         ),
     )
+    ingest.add_argument(
+        "--no-loss-report",
+        dest="no_loss_report",
+        action="store_true",
+        help=(
+            "disable adapter LossReport sidecar (ticket #000022). "
+            "Default: enabled. Sidecar — toggling does NOT invalidate "
+            "QA cache_keys"
+        ),
+    )
+    ingest.add_argument(
+        "--no-loss-excerpts",
+        dest="no_loss_excerpts",
+        action="store_true",
+        help=(
+            "drop sample_excerpt content from LossReport rows "
+            "(PII-paranoid mode). sample_hash stays populated"
+        ),
+    )
+    ingest.add_argument(
+        "--loss-excerpt-bytes",
+        dest="loss_excerpt_bytes",
+        type=int,
+        default=200,
+        help="max excerpt byte length (default 200)",
+    )
     ingest.set_defaults(func=_cmd_ingest)
 
     search = sub.add_parser("search", help="keyword search (UNGROUNDED audit mode)")
@@ -3995,6 +4116,43 @@ def build_parser() -> argparse.ArgumentParser:
     )
     inspect_cmd.set_defaults(func=_cmd_inspect)
 
+    losses_cmd = sub.add_parser(
+        "losses",
+        help=(
+            "list adapter LossReport sidecar rows (ticket #000022). "
+            "Read-only; never enters proof path"
+        ),
+    )
+    losses_cmd.add_argument(
+        "--document-root", dest="document_root", default=None,
+        help="filter to one document_root (hex)",
+    )
+    losses_cmd.add_argument(
+        "--chunk-id", dest="chunk_id", type=int, default=None,
+        help="filter to one chunk_id",
+    )
+    losses_cmd.add_argument(
+        "--kind", default=None,
+        help="filter to one loss_kind (ref_tag, file_link, html_chrome, ...)",
+    )
+    losses_cmd.add_argument(
+        "--stage", default=None,
+        help="filter to one stage (wikitext_base, html_normalize, ingest)",
+    )
+    losses_cmd.add_argument(
+        "--summary", action="store_true",
+        help="aggregate by (stage, loss_kind, loss_mode)",
+    )
+    losses_cmd.add_argument(
+        "--limit", type=int, default=200,
+        help="row cap for non-summary mode (default 200)",
+    )
+    losses_cmd.add_argument(
+        "--json", action="store_true",
+        help="emit raw rows as JSON (default: human render)",
+    )
+    losses_cmd.set_defaults(func=_cmd_losses)
+
     prov_cmd = sub.add_parser(
         "providence",
         help="list or falsify providence_cache records",
diff --git a/arborist/ingest.py b/arborist/ingest.py
index 025e719..b2e14f4 100644
--- a/arborist/ingest.py
+++ b/arborist/ingest.py
@@ -63,6 +63,9 @@ def ingest_source(
     batch_size: int = DEFAULT_BATCH_SIZE,
     resume: bool = False,
     progress: Progress | None = None,
+    loss_report_enabled: bool = True,
+    loss_report_excerpts: bool = True,
+    loss_report_max_excerpt_bytes: int = 200,
 ) -> IngestStats:
     """Ingest every document the source yields. Returns counts.
 
@@ -91,7 +94,14 @@ def ingest_source(
     def flush() -> None:
         if not batch:
             return
-        inserted, skipped = _flush_batch(conn, batch, chunker.name)
+        inserted, skipped = _flush_batch(
+            conn,
+            batch,
+            chunker.name,
+            loss_report_enabled=loss_report_enabled,
+            loss_report_excerpts=loss_report_excerpts,
+            loss_report_max_excerpt_bytes=loss_report_max_excerpt_bytes,
+        )
         stats.inserted += inserted
         stats.skipped_duplicate += skipped
         batch.clear()
@@ -142,6 +152,10 @@ def _flush_batch(
     conn: sqlite3.Connection,
     batch: list[tuple[Document, _DocArtifacts]],
     chunker_name: str,
+    *,
+    loss_report_enabled: bool = True,
+    loss_report_excerpts: bool = True,
+    loss_report_max_excerpt_bytes: int = 200,
 ) -> tuple[int, int]:
     """Bulk-insert the whole batch. Returns (inserted, skipped_duplicate).
 
@@ -197,6 +211,19 @@ def _flush_batch(
         edge_rows: list[tuple] = []
         audit_events: list[dict] = []
         edges_to_upsert: list[tuple[str, Document]] = []
+        # (chunk_id, document_root, [LossEvent...]) collected during the
+        # main loop, persisted at end-of-batch in one executemany. See
+        # ticket #000022 §3.5. Sidecar — does NOT enter audit_events.
+        loss_persist: list[tuple[int, str, list]] = []
+
+        loss_policy_hash = ""
+        if loss_report_enabled:
+            from arborist.sources.loss_report import compute_loss_report_policy_hash
+            loss_policy_hash = compute_loss_report_policy_hash(
+                enabled=loss_report_enabled,
+                excerpts=loss_report_excerpts,
+                max_excerpt_bytes=loss_report_max_excerpt_bytes,
+            )
 
         for doc, art in batch:
             if art.document_root in existing or art.document_root in inserted_this_batch:
@@ -220,15 +247,62 @@ def _flush_batch(
                     ingest_ts,
                 )
             )
+            is_wikitext_source = doc.source_type.startswith("wikipedia_")
+            first_chunk_id_for_doc: int | None = None
             for i, c in enumerate(art.chunk_strs):
                 chunk_id = next_chunk_id
                 next_chunk_id += 1
+                if first_chunk_id_for_doc is None:
+                    first_chunk_id_for_doc = chunk_id
                 chunk_rows.append(
                     (chunk_id, art.document_root, i, art.leaves[i].hex(), pack_chunk(c))
                 )
                 # Contentless FTS5 indexes the plaintext but stores no copy;
                 # rowid must equal chunks.chunk_id so search-time JOINs line up.
                 fts_rows.append((chunk_id, c))
+
+                # Per-chunk wikitext_base loss reporting. Run to_base()
+                # eagerly with a collector to capture what the LLM-side
+                # path would later drop. Output is discarded —
+                # chunks.content stays raw wikitext per the
+                # document_root invariant.
+                if loss_report_enabled and is_wikitext_source:
+                    try:
+                        from arborist.sources.loss_report import LossCollector
+                        from arborist.wikitext import (
+                            ADAPTER_NAME as _WT_ADAPTER,
+                            BASE_VERSION as _WT_VERSION,
+                            to_base as _wt_to_base,
+                        )
+                        collector = LossCollector(
+                            excerpts_enabled=loss_report_excerpts,
+                            max_excerpt_bytes=loss_report_max_excerpt_bytes,
+                            adapter_name=_WT_ADAPTER,
+                            adapter_version=_WT_VERSION,
+                        )
+                        _wt_to_base(c, loss_collector=collector)
+                        events = collector.events()
+                        if events:
+                            loss_persist.append(
+                                (chunk_id, art.document_root, events)
+                            )
+                    except ImportError:
+                        # mwparserfromhell not installed — skip silently.
+                        # LossReport is additive metadata, never a gate.
+                        pass
+
+            # Document-scope losses (e.g. HTML normalize) anchor to the
+            # first chunk_id by convention. See ticket #000022 §3.4.
+            if (
+                loss_report_enabled
+                and first_chunk_id_for_doc is not None
+                and isinstance(doc.extra, dict)
+            ):
+                doc_events = doc.extra.get("loss_events")
+                if doc_events:
+                    loss_persist.append(
+                        (first_chunk_id_for_doc, art.document_root, list(doc_events))
+                    )
             for layer_idx in range(1, len(art.tree.layers)):
                 for node_idx, h in enumerate(art.tree.layers[layer_idx]):
                     merkle_rows.append(
@@ -286,6 +360,22 @@ def _flush_batch(
                 merkle_rows,
             )
 
+        # 3.5) Adapter LossReport sidecar (ticket #000022). Persisted
+        # under the same transaction as chunks so an auditor never sees
+        # a chunk_id without its loss rows. Sidecar — does NOT enter
+        # audit_events / cache_key / document_root.
+        if loss_persist:
+            from arborist.sources.loss_report import record_losses
+            for ck, drt, evs in loss_persist:
+                record_losses(
+                    conn,
+                    chunk_id=ck,
+                    document_root=drt,
+                    events=evs,
+                    loss_report_policy_hash=loss_policy_hash,
+                    ts=ingest_ts,
+                )
+
         # 4) Edges: collect all wikilinks across the batch and resolve in
         #    one SELECT. Then one executemany.
         _flush_edges(conn, edges_to_upsert)
diff --git a/arborist/sources/html_page.py b/arborist/sources/html_page.py
index 2a8dcd9..16cfa9e 100644
--- a/arborist/sources/html_page.py
+++ b/arborist/sources/html_page.py
@@ -12,7 +12,7 @@ import re
 import urllib.parse
 import urllib.robotparser
 from pathlib import Path
-from typing import Iterable, Iterator
+from typing import TYPE_CHECKING, Iterable, Iterator
 
 try:
     import httpx
@@ -25,28 +25,93 @@ except ImportError as e:  # pragma: no cover
 from arborist.document import Document, Edge
 from arborist.source import Source
 
+if TYPE_CHECKING:
+    from arborist.sources.loss_report import LossCollector
+
 
 USER_AGENT = "arborist/0.0.1 (+https://unturf.com)"
 NOISE_SELECTORS = ("script", "style", "noscript", "nav", "header", "footer", "aside")
+NORMALIZE_VERSION = "html-normalize-v1"
+ADAPTER_NAME = "HtmlPageSource"
+
+# Loss-kind taxonomy per ticket #000022 §2.1.1. Free-string in v0; promoted
+# to enum after >=3 adapters. ``html_chrome`` is heuristic — selectolax may
+# leave residual nav text on pages that don't tag with semantic elements;
+# auditors should treat the kind as advisory, not authoritative.
+_NOISE_LOSS_KINDS = {
+    "script": "script_block",
+    "style": "style_block",
+    "noscript": "html_chrome",
+    "nav": "html_chrome",
+    "header": "html_chrome",
+    "footer": "html_chrome",
+    "aside": "html_chrome",
+}
 
 
-def _normalize_text(text: str) -> str:
+def _normalize_text(
+    text: str,
+    *,
+    loss_collector: "LossCollector | None" = None,
+) -> str:
+    pre_len = (
+        len(text.encode("utf-8", errors="surrogatepass"))
+        if loss_collector is not None
+        else 0
+    )
     text = re.sub(r"[ \t]+", " ", text)
     text = re.sub(r"\n{3,}", "\n\n", text)
-    return text.strip()
+    text = text.strip()
+    if loss_collector is not None:
+        post_len = len(text.encode("utf-8", errors="surrogatepass"))
+        loss_collector.record_delta(
+            stage="html_normalize",
+            canonicalization_version=NORMALIZE_VERSION,
+            loss_kind="whitespace_run",
+            loss_mode="normalize",
+            bytes_delta=pre_len - post_len,
+        )
+    return text
 
 
-def parse_html(url: str, html: str, source_type: str = "html") -> Document | None:
-    """Pure parse function. Separated so tests can run without network."""
+def parse_html(
+    url: str,
+    html: str,
+    source_type: str = "html",
+    *,
+    loss_collector: "LossCollector | None" = None,
+) -> Document | None:
+    """Pure parse function. Separated so tests can run without network.
+
+    When ``loss_collector`` is provided, drops from noise-selector
+    decomposition (``<script>``, ``<style>``, ``<nav>``, etc.) and
+    whitespace normalization are recorded against the collector. Output
+    bytes remain bit-identical to the no-collector path. Default
+    ``None`` keeps callers stable.
+    """
     tree = HTMLParser(html)
     for sel in NOISE_SELECTORS:
         for node in tree.css(sel):
+            if loss_collector is not None:
+                kind = _NOISE_LOSS_KINDS.get(sel, "html_chrome")
+                dropped_html = node.html or ""
+                if dropped_html:
+                    loss_collector.add(
+                        stage="html_normalize",
+                        canonicalization_version=NORMALIZE_VERSION,
+                        loss_kind=kind,
+                        loss_mode="pure_drop",
+                        dropped=dropped_html,
+                    )
             node.decompose()
 
     body = tree.css_first("body") or tree.root
     if body is None:
         return None
-    text = _normalize_text(body.text(separator="\n", strip=True))
+    text = _normalize_text(
+        body.text(separator="\n", strip=True),
+        loss_collector=loss_collector,
+    )
     if not text:
         return None
 
@@ -71,12 +136,22 @@ def parse_html(url: str, html: str, source_type: str = "html") -> Document | Non
         seen.add(key)
         edges.append(Edge(edge_type="hyperlink", dst_uri=dst_uri, anchor=anchor or None))
 
+    extra: dict = {}
+    if loss_collector is not None:
+        events = loss_collector.events()
+        if events:
+            # Document-scope losses anchor to the doc's first chunk at
+            # ingest time. We stash them in extra; ingest reads and
+            # persists. See ticket #000022 §3.4.
+            extra["loss_events"] = events
+
     return Document(
         uri=url,
         content=text,
         source_type=source_type,
         title=title,
         edges=edges,
+        extra=extra,
     )
 
 
@@ -91,10 +166,16 @@ class HtmlPageSource(Source):
         *,
         respect_robots: bool = True,
         timeout: float = 30.0,
+        loss_report_enabled: bool = True,
+        loss_report_excerpts: bool = True,
+        loss_report_max_excerpt_bytes: int = 200,
     ):
         self.urls = list(urls)
         self.respect_robots = respect_robots
         self.timeout = timeout
+        self.loss_report_enabled = loss_report_enabled
+        self.loss_report_excerpts = loss_report_excerpts
+        self.loss_report_max_excerpt_bytes = loss_report_max_excerpt_bytes
         self._robots_cache: dict[str, urllib.robotparser.RobotFileParser] = {}
 
     @classmethod
@@ -123,7 +204,21 @@ class HtmlPageSource(Source):
                 ctype = resp.headers.get("content-type", "").lower()
                 if "html" not in ctype and "xml" not in ctype:
                     continue
-                doc = parse_html(str(resp.url), resp.text, self.source_type)
+                collector = None
+                if self.loss_report_enabled:
+                    from arborist.sources.loss_report import LossCollector
+                    collector = LossCollector(
+                        excerpts_enabled=self.loss_report_excerpts,
+                        max_excerpt_bytes=self.loss_report_max_excerpt_bytes,
+                        adapter_name=ADAPTER_NAME,
+                        adapter_version=NORMALIZE_VERSION,
+                    )
+                doc = parse_html(
+                    str(resp.url),
+                    resp.text,
+                    self.source_type,
+                    loss_collector=collector,
+                )
                 if doc is not None:
                     yield doc
 
diff --git a/arborist/sources/loss_report.py b/arborist/sources/loss_report.py
new file mode 100644
index 0000000..f5657b8
--- /dev/null
+++ b/arborist/sources/loss_report.py
@@ -0,0 +1,329 @@
+"""Adapter LossReport sidecar (ticket #000022).
+
+Typed loss ledger for what bytes the adapter / canonicalizer dropped,
+transformed, or normalized on the way from raw bytes to the prose the
+model sees. SIDECAR ONLY: never enters ``cache_key``, ``document_root``,
+``run_dag_root``, or the ``audit_events`` chain.
+
+Loss policy lives in its own ``loss_report_policy_hash`` (computed
+here) — separate from the QA ``governance_policy_hash``, so toggling
+reporting does NOT invalidate prior cache entries. See ticket §3.7.
+
+Public surface:
+
+    LossEvent       — frozen dataclass, one per (loss_kind, chunk, stage).
+    LossCollector   — accumulates per-kind aggregates during a normalizer
+                      pass; merging duplicate kinds inside one chunk.
+    record_losses   — batched, idempotent persistence.
+    compute_loss_report_policy_hash — pure hash of the three policy fields.
+
+The module has zero non-stdlib deps so callers in adapters / wikitext can
+import it without dragging the wikitext / html extras.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import sqlite3
+import time
+from dataclasses import dataclass, field
+from typing import Iterable, Optional
+
+
+LOSS_REPORT_VERSION = "loss-report-v1"
+
+DEFAULT_MAX_EXCERPT_BYTES = 200
+
+VALID_LOSS_MODES = frozenset({"pure_drop", "transform", "quarantine", "normalize"})
+
+
+@dataclass(frozen=True)
+class LossEvent:
+    """One aggregated loss event for a (chunk, stage, kind) tuple.
+
+    ``bytes_dropped`` semantics depend on ``loss_mode``:
+
+      pure_drop / quarantine — bytes removed from the prose stream;
+                               participates in the byte-conservation
+                               property test (§3.8).
+      transform / normalize  — byte delta only; excluded from the
+                               property test because content was
+                               rewritten, not deleted.
+
+    ``sample_excerpt`` is None when the policy disables excerpts;
+    ``sample_hash`` stays populated either way so loss-signature
+    recurrence remains detectable in PII-safe mode.
+    """
+
+    stage: str
+    canonicalization_version: str
+    loss_kind: str
+    loss_mode: str
+    bytes_dropped: int
+    occurrence_count: int
+    input_length_bytes: Optional[int] = None
+    output_length_bytes: Optional[int] = None
+    sample_excerpt: Optional[str] = None
+    sample_hash: Optional[bytes] = None
+    adapter_name: Optional[str] = None
+    adapter_version: Optional[str] = None
+
+    def __post_init__(self) -> None:
+        if self.loss_mode not in VALID_LOSS_MODES:
+            raise ValueError(
+                f"loss_mode {self.loss_mode!r} not in {sorted(VALID_LOSS_MODES)}"
+            )
+
+
+def _truncate(s: str, limit: int) -> str:
+    """UTF-8-aware byte truncation. Caller passes a byte limit; we return
+    a string that encodes to <= limit bytes. Cuts on character boundary
+    so the excerpt remains decodable."""
+    encoded = s.encode("utf-8", errors="surrogatepass")
+    if len(encoded) <= limit:
+        return s
+    cut = encoded[:limit]
+    while cut:
+        try:
+            return cut.decode("utf-8")
+        except UnicodeDecodeError:
+            cut = cut[:-1]
+    return ""
+
+
+def _sha256_bytes(data: bytes) -> bytes:
+    return hashlib.sha256(data).digest()
+
+
+@dataclass
+class LossCollector:
+    """Per-pass accumulator. One collector per (chunk, normalizer-pass).
+
+    ``add()`` is the hot path; idempotent only at the (stage, kind) level
+    — duplicate adds for the same kind merge by summing ``bytes_dropped``
+    and ``occurrence_count``. The first sample seen wins for excerpt /
+    hash (cheap; matches the §2.1 "representative excerpt" wording).
+
+    ``events()`` returns the frozen `LossEvent` list once the pass
+    completes. Subsequent ``add()`` after ``events()`` is allowed
+    (collector stays mutable) — useful when one collector spans multiple
+    micro-passes within a single canonicalizer.
+    """
+
+    excerpts_enabled: bool = True
+    max_excerpt_bytes: int = DEFAULT_MAX_EXCERPT_BYTES
+    adapter_name: Optional[str] = None
+    adapter_version: Optional[str] = None
+    input_length_bytes: Optional[int] = None
+    output_length_bytes: Optional[int] = None
+    _agg: dict[tuple[str, str, str], dict] = field(default_factory=dict)
+
+    def add(
+        self,
+        *,
+        stage: str,
+        canonicalization_version: str,
+        loss_kind: str,
+        loss_mode: str,
+        dropped: str | bytes,
+        occurrences: int = 1,
+    ) -> None:
+        if loss_mode not in VALID_LOSS_MODES:
+            raise ValueError(
+                f"loss_mode {loss_mode!r} not in {sorted(VALID_LOSS_MODES)}"
+            )
+        if isinstance(dropped, str):
+            dropped_bytes = dropped.encode("utf-8", errors="surrogatepass")
+        else:
+            dropped_bytes = dropped
+        n_bytes = len(dropped_bytes)
+
+        key = (stage, canonicalization_version, loss_kind)
+        slot = self._agg.get(key)
+        if slot is None:
+            sample_text: Optional[str]
+            try:
+                decoded = dropped_bytes.decode("utf-8", errors="replace")
+            except Exception:
+                decoded = ""
+            if self.excerpts_enabled:
+                sample_text = _truncate(decoded, self.max_excerpt_bytes)
+            else:
+                sample_text = None
+            slot = {
+                "stage": stage,
+                "canonicalization_version": canonicalization_version,
+                "loss_kind": loss_kind,
+                "loss_mode": loss_mode,
+                "bytes_dropped": 0,
+                "occurrence_count": 0,
+                "sample_excerpt": sample_text,
+                "sample_hash": _sha256_bytes(
+                    dropped_bytes[: self.max_excerpt_bytes]
+                ),
+            }
+            self._agg[key] = slot
+        elif slot["loss_mode"] != loss_mode:
+            raise ValueError(
+                f"loss_mode mismatch on duplicate add for {key!r}: "
+                f"existing={slot['loss_mode']!r} new={loss_mode!r}"
+            )
+        slot["bytes_dropped"] += n_bytes
+        slot["occurrence_count"] += occurrences
+
+    def record_delta(
+        self,
+        *,
+        stage: str,
+        canonicalization_version: str,
+        loss_kind: str,
+        loss_mode: str,
+        bytes_delta: int,
+        occurrences: int = 1,
+    ) -> None:
+        """Record a byte-length delta with no associated content sample.
+
+        Use for ``transform`` or ``normalize`` events where bytes were
+        rewritten in place (e.g. ``strip_code``, whitespace collapse) and
+        there is no single span to capture. ``bytes_delta`` aggregates
+        across multiple ``record_delta`` calls for the same kind.
+        """
+        if loss_mode not in VALID_LOSS_MODES:
+            raise ValueError(
+                f"loss_mode {loss_mode!r} not in {sorted(VALID_LOSS_MODES)}"
+            )
+        if bytes_delta <= 0:
+            return
+        key = (stage, canonicalization_version, loss_kind)
+        slot = self._agg.get(key)
+        if slot is None:
+            slot = {
+                "stage": stage,
+                "canonicalization_version": canonicalization_version,
+                "loss_kind": loss_kind,
+                "loss_mode": loss_mode,
+                "bytes_dropped": 0,
+                "occurrence_count": 0,
+                "sample_excerpt": None,
+                "sample_hash": None,
+            }
+            self._agg[key] = slot
+        elif slot["loss_mode"] != loss_mode:
+            raise ValueError(
+                f"loss_mode mismatch on duplicate add for {key!r}: "
+                f"existing={slot['loss_mode']!r} new={loss_mode!r}"
+            )
+        slot["bytes_dropped"] += int(bytes_delta)
+        slot["occurrence_count"] += occurrences
+
+    def set_lengths(self, *, input_bytes: int, output_bytes: int) -> None:
+        """Record the chunk-level input/output sizes for the byte-
+        conservation property test. Called once per pass after
+        normalization completes."""
+        self.input_length_bytes = input_bytes
+        self.output_length_bytes = output_bytes
+
+    def events(self) -> list[LossEvent]:
+        """Snapshot the accumulator as a list of frozen `LossEvent`s."""
+        out: list[LossEvent] = []
+        for slot in self._agg.values():
+            out.append(
+                LossEvent(
+                    stage=slot["stage"],
+                    canonicalization_version=slot["canonicalization_version"],
+                    loss_kind=slot["loss_kind"],
+                    loss_mode=slot["loss_mode"],
+                    bytes_dropped=slot["bytes_dropped"],
+                    occurrence_count=slot["occurrence_count"],
+                    input_length_bytes=self.input_length_bytes,
+                    output_length_bytes=self.output_length_bytes,
+                    sample_excerpt=slot["sample_excerpt"],
+                    sample_hash=slot["sample_hash"],
+                    adapter_name=self.adapter_name,
+                    adapter_version=self.adapter_version,
+                )
+            )
+        return out
+
+
+def compute_loss_report_policy_hash(
+    *,
+    enabled: bool,
+    excerpts: bool,
+    max_excerpt_bytes: int,
+    version: str = LOSS_REPORT_VERSION,
+) -> str:
+    """Hash the three loss-reporting policy fields. Pure function.
+
+    Returns 64-char hex sha256 over a canonical JSON. Stored on each
+    ``adapter_loss_reports`` row so an auditor can correlate policy
+    changes with loss data. NOT folded into ``governance_policy_hash``.
+    """
+    body = {
+        "version": version,
+        "enabled": bool(enabled),
+        "excerpts": bool(excerpts),
+        "max_excerpt_bytes": int(max_excerpt_bytes),
+    }
+    canonical = json.dumps(
+        body, sort_keys=True, separators=(",", ":"), ensure_ascii=False
+    )
+    return hashlib.sha256(canonical.encode("utf-8")).hexdigest()
+
+
+def record_losses(
+    conn: sqlite3.Connection,
+    *,
+    chunk_id: int,
+    document_root: str,
+    events: Iterable[LossEvent],
+    loss_report_policy_hash: str,
+    ts: int | None = None,
+) -> int:
+    """Batched, idempotent insert of `LossEvent`s for one chunk.
+
+    Idempotency: PK is (chunk_id, stage, canonicalization_version,
+    loss_kind). Re-running the same normalizer over the same chunk
+    is a no-op via INSERT OR REPLACE.
+
+    Caller wraps in a transaction (or this runs inside the ingest
+    batch's transaction). Returns the row count touched.
+    """
+    if ts is None:
+        ts = int(time.time())
+    rows: list[tuple] = []
+    for ev in events:
+        rows.append(
+            (
+                chunk_id,
+                document_root,
+                ev.stage,
+                ev.canonicalization_version,
+                ev.loss_kind,
+                ev.loss_mode,
+                ev.bytes_dropped,
+                ev.occurrence_count,
+                ev.input_length_bytes,
+                ev.output_length_bytes,
+                ev.sample_excerpt,
+                ev.sample_hash.hex() if ev.sample_hash is not None else None,
+                ev.adapter_name,
+                ev.adapter_version,
+                loss_report_policy_hash,
+                ts,
+            )
+        )
+    if not rows:
+        return 0
+    conn.executemany(
+        "INSERT OR REPLACE INTO adapter_loss_reports "
+        "(chunk_id, document_root, stage, canonicalization_version, "
+        " loss_kind, loss_mode, bytes_dropped, occurrence_count, "
+        " input_length_bytes, output_length_bytes, sample_excerpt, "
+        " sample_hash, adapter_name, adapter_version, "
+        " loss_report_policy_hash, created_at) "
+        "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+        rows,
+    )
+    return len(rows)
diff --git a/arborist/store.py b/arborist/store.py
index d9c0d24..5e9eed2 100644
--- a/arborist/store.py
+++ b/arborist/store.py
@@ -403,6 +403,63 @@ CREATE TABLE IF NOT EXISTS concept_token_idf (
     derived_at  INTEGER NOT NULL
 );
 CREATE INDEX IF NOT EXISTS idx_token_idf_freq ON concept_token_idf(doc_freq);
+
+-- Adapter LossReport sidecar (ticket #000022). Per-chunk record of what
+-- bytes the adapter / canonicalizer dropped, transformed, or normalized
+-- on the way from raw bytes to the prose the model sees.
+--
+-- DESIGN: SIDECAR ONLY. This table never enters cache_key, document_root,
+-- run_dag_root, or audit_events.event_hash preimage. Its policy lives in
+-- ``loss_report_policy_hash`` (column below) — separate from the QA
+-- ``governance_policy_hash`` so toggling reporting does NOT invalidate
+-- prior cache entries. See ticket §3.7.
+--
+-- ``loss_mode`` semantics (closed enum):
+--   'pure_drop'   content removed entirely (e.g. <ref> blocks).
+--                 sum(bytes_dropped) MUST be <= input_length_bytes.
+--   'transform'   content rewritten to different bytes (e.g.
+--                 [[Velociraptor]] -> Velociraptor). bytes_dropped
+--                 records a delta, not a deletion. Excluded from
+--                 the byte-conservation property test.
+--   'quarantine'  content preserved elsewhere but withheld from prose.
+--                 Reserved; no v0 emitter.
+--   'normalize'   semantically low-content formatting normalization
+--                 (whitespace runs, newline collapse, &nbsp; runs).
+--                 Excluded from byte-conservation accounting.
+--
+-- ``loss_kind`` is free-string in v0 (per ticket §4 out-of-scope) so
+-- adapter authors can mint new kinds. Promotion to enum after >=3
+-- adapters are in tree.
+--
+-- Document-scope losses (e.g. HTML _normalize_text drops that happen
+-- before chunking) are anchored to chunk_id of the lowest-idx chunk
+-- of the document by convention.
+CREATE TABLE IF NOT EXISTS adapter_loss_reports (
+    chunk_id                 INTEGER NOT NULL,
+    document_root            TEXT NOT NULL,
+    stage                    TEXT NOT NULL,
+    canonicalization_version TEXT NOT NULL,
+    loss_kind                TEXT NOT NULL,
+    loss_mode                TEXT NOT NULL
+                                CHECK (loss_mode IN ('pure_drop','transform','quarantine','normalize')),
+    bytes_dropped            INTEGER NOT NULL,
+    occurrence_count         INTEGER NOT NULL,
+    input_length_bytes       INTEGER,
+    output_length_bytes      INTEGER,
+    sample_excerpt           TEXT,
+    sample_hash              TEXT,
+    adapter_name             TEXT,
+    adapter_version          TEXT,
+    loss_report_policy_hash  TEXT NOT NULL,
+    created_at               INTEGER NOT NULL,
+    PRIMARY KEY (chunk_id, stage, canonicalization_version, loss_kind)
+);
+CREATE INDEX IF NOT EXISTS idx_adapter_loss_doc
+    ON adapter_loss_reports(document_root, stage);
+CREATE INDEX IF NOT EXISTS idx_adapter_loss_kind
+    ON adapter_loss_reports(loss_kind, stage);
+CREATE INDEX IF NOT EXISTS idx_adapter_loss_chunk
+    ON adapter_loss_reports(chunk_id, stage);
 """
 
 
@@ -427,6 +484,7 @@ def connect(db_path: Path | str = DEFAULT_DB_PATH) -> sqlite3.Connection:
     _migrate_selfmodel_tables(conn)
     _migrate_capital_ledger(conn)
     _migrate_memory_root(conn)
+    _migrate_adapter_loss_reports(conn)
     conn.execute("PRAGMA synchronous = NORMAL")
     conn.execute("PRAGMA cache_size = -65536")
     conn.execute("PRAGMA temp_store = MEMORY")
@@ -704,6 +762,54 @@ def _migrate_memory_root(conn: sqlite3.Connection) -> None:
         )
 
 
+def _migrate_adapter_loss_reports(conn: sqlite3.Connection) -> None:
+    """Forward-migrate to add adapter_loss_reports (ticket #000022).
+
+    Sidecar — does NOT enter cache_key, document_root, run_dag_root,
+    audit_events.event_hash preimage. Idempotent table-existence probe,
+    then CREATE-if-missing, mirroring the established migration pattern.
+    """
+    row = conn.execute(
+        "SELECT name FROM sqlite_master "
+        "WHERE type='table' AND name='adapter_loss_reports'"
+    ).fetchone()
+    if row is None:
+        conn.execute(
+            "CREATE TABLE adapter_loss_reports ("
+            " chunk_id                 INTEGER NOT NULL,"
+            " document_root            TEXT NOT NULL,"
+            " stage                    TEXT NOT NULL,"
+            " canonicalization_version TEXT NOT NULL,"
+            " loss_kind                TEXT NOT NULL,"
+            " loss_mode                TEXT NOT NULL"
+            "    CHECK (loss_mode IN ('pure_drop','transform','quarantine','normalize')),"
+            " bytes_dropped            INTEGER NOT NULL,"
+            " occurrence_count         INTEGER NOT NULL,"
+            " input_length_bytes       INTEGER,"
+            " output_length_bytes      INTEGER,"
+            " sample_excerpt           TEXT,"
+            " sample_hash              TEXT,"
+            " adapter_name             TEXT,"
+            " adapter_version          TEXT,"
+            " loss_report_policy_hash  TEXT NOT NULL,"
+            " created_at               INTEGER NOT NULL,"
+            " PRIMARY KEY (chunk_id, stage, canonicalization_version, loss_kind)"
+            ")"
+        )
+        conn.execute(
+            "CREATE INDEX idx_adapter_loss_doc "
+            "ON adapter_loss_reports(document_root, stage)"
+        )
+        conn.execute(
+            "CREATE INDEX idx_adapter_loss_kind "
+            "ON adapter_loss_reports(loss_kind, stage)"
+        )
+        conn.execute(
+            "CREATE INDEX idx_adapter_loss_chunk "
+            "ON adapter_loss_reports(chunk_id, stage)"
+        )
+
+
 def _migrate_mesh_peer_chains(conn: sqlite3.Connection) -> None:
     """Forward-migrate pre-mesh-fork-detection shards.
 
@@ -966,6 +1072,7 @@ _SHARDABLE_TABLES = (
     "falsifications",
     "concept_relations",
     "concept_token_idf",
+    "adapter_loss_reports",
 )
 
 # Per-table column lists for cross-shard UNION views. The `chunks` table
diff --git a/arborist/wikitext.py b/arborist/wikitext.py
index 9176fa1..2e00107 100644
--- a/arborist/wikitext.py
+++ b/arborist/wikitext.py
@@ -39,6 +39,7 @@ Optional dependency. Install with ``pip install arborist[wikitext]``.
 from __future__ import annotations
 
 import re
+from typing import TYPE_CHECKING
 
 try:
     import mwparserfromhell as _mw
@@ -48,8 +49,12 @@ except ImportError as e:  # pragma: no cover
         "pip install 'arborist[wikitext]'"
     ) from e
 
+if TYPE_CHECKING:
+    from arborist.sources.loss_report import LossCollector
+
 
 BASE_VERSION = "wikitext-base-v1"
+ADAPTER_NAME = "WikitextBase"
 
 # Namespaces whose links carry no prose. ``File`` and ``Image`` are the
 # same target type (image inclusion); MediaWiki accepts both prefixes.
@@ -62,12 +67,22 @@ _TRAILING_WS = re.compile(r" +\n")
 _BLANK_LINES = re.compile(r"\n{3,}")
 
 
-def to_base(raw: str) -> str:
+def to_base(
+    raw: str,
+    *,
+    loss_collector: "LossCollector | None" = None,
+) -> str:
     """Convert raw wikitext to base prose. Deterministic. Idempotent.
 
     Empty / whitespace-only input returns ``""``. Non-wikitext input
     (already-clean prose) round-trips unchanged modulo whitespace
     collapsing.
+
+    When ``loss_collector`` is provided, every drop / transform /
+    normalize step records a ``LossEvent`` against the collector. The
+    output bytes remain bit-identical to the no-collector path —
+    LossReport is additive metadata, never a gate. Default ``None``
+    keeps the LLM-call path (verifier + query + runner) unchanged.
     """
     if not raw or not raw.strip():
         return ""
@@ -78,12 +93,22 @@ def to_base(raw: str) -> str:
     # the tag name (case-insensitive) so that <REF>, <Ref>, etc. all go.
     for tag in list(code.filter_tags()):
         if str(tag.tag).strip().lower() == "ref":
+            tag_text = str(tag)
             try:
                 code.remove(tag)
             except ValueError:
                 # Tag was already removed via a parent node. mwparserfromhell
                 # raises rather than no-op'ing; we swallow it.
-                pass
+                continue
+            if loss_collector is not None:
+                kind = "self_closing_ref_tag" if getattr(tag, "self_closing", False) else "ref_tag"
+                loss_collector.add(
+                    stage="wikitext_base",
+                    canonicalization_version=BASE_VERSION,
+                    loss_kind=kind,
+                    loss_mode="pure_drop",
+                    dropped=tag_text,
+                )
 
     # Drop File: / Image: / Category: wikilinks. Image captions sometimes
     # contain useful prose ("thumb|250px|<caption>") but the technical
@@ -93,18 +118,69 @@ def to_base(raw: str) -> str:
         if ":" in title:
             ns = title.split(":", 1)[0].strip().lower()
             if ns in _DROP_NAMESPACES:
+                link_text = str(link)
                 try:
                     code.remove(link)
                 except ValueError:
-                    pass
+                    continue
+                if loss_collector is not None:
+                    kind = {
+                        "file": "file_link",
+                        "image": "image_link",
+                        "category": "category_link",
+                    }[ns]
+                    loss_collector.add(
+                        stage="wikitext_base",
+                        canonicalization_version=BASE_VERSION,
+                        loss_kind=kind,
+                        loss_mode="pure_drop",
+                        dropped=link_text,
+                    )
 
+    pre_strip_len = (
+        len(str(code).encode("utf-8", errors="surrogatepass"))
+        if loss_collector is not None
+        else 0
+    )
     base = code.strip_code(normalize=True, collapse=True)
+    if loss_collector is not None:
+        # strip_code rewrites surviving wikilinks/templates/HTML to their
+        # display text — bytes change, content is preserved as text.
+        # Recorded as 'transform' (excluded from byte-conservation
+        # property test).
+        post_strip_len = len(base.encode("utf-8", errors="surrogatepass"))
+        loss_collector.record_delta(
+            stage="wikitext_base",
+            canonicalization_version=BASE_VERSION,
+            loss_kind="strip_code_transform",
+            loss_mode="transform",
+            bytes_delta=pre_strip_len - post_strip_len,
+        )
 
     # Whitespace normalization — keeps paragraph breaks, drops runs.
+    pre_ws_len = (
+        len(base.encode("utf-8", errors="surrogatepass"))
+        if loss_collector is not None
+        else 0
+    )
     base = _WS_RUN.sub(" ", base)
     base = _TRAILING_WS.sub("\n", base)
     base = _BLANK_LINES.sub("\n\n", base)
-    return base.strip()
+    base = base.strip()
+    if loss_collector is not None:
+        post_ws_len = len(base.encode("utf-8", errors="surrogatepass"))
+        loss_collector.record_delta(
+            stage="wikitext_base",
+            canonicalization_version=BASE_VERSION,
+            loss_kind="whitespace_run",
+            loss_mode="normalize",
+            bytes_delta=pre_ws_len - post_ws_len,
+        )
+        loss_collector.set_lengths(
+            input_bytes=len(raw.encode("utf-8", errors="surrogatepass")),
+            output_bytes=len(base.encode("utf-8", errors="surrogatepass")),
+        )
+    return base
 
 
 def extract_wikilinks(raw: str) -> list[tuple[str, str | None]]:
diff --git a/docs/TICKETS.md b/docs/TICKETS.md
index b8cde0e..d9d34f5 100644
--- a/docs/TICKETS.md
+++ b/docs/TICKETS.md
@@ -60,7 +60,7 @@ Newest first. Update on every open/close.
 | #000025  | 5F battery (Function · Finetuning · Falsification · Formulate · Feedback Loop) | open · awaiting go/no-go | 2026-05-07 | —         |
 | #000024  | 5T Phase 1b + Dav1DPrometheus vocabulary alignment | open · awaiting go/no-go | 2026-05-07 | —         |
 | #000023  | 5S Phase 1b: Syllogism · Synthesis · Semiotics | open · awaiting go/no-go | 2026-05-07 | —         |
-| #000022  | Adapter LossReport (PRD I9 analogue)           | open · awaiting go/no-go | 2026-05-07 | —         |
+| #000022  | Adapter LossReport (PRD I9 analogue)           | closed · landed 2026-05-07 | 2026-05-07 | —         |
 | #000021  | 5S/5T/5R benchmark fixtures + harness          | in progress · Phase 1a landed 2026-05-07 | 2026-05-07 | —         |
 | #000020  | Capital-cost ledger (8-capital queues)         | closed · landed 2026-05-07 | 2026-05-07 | —         |
 | #000019  | Specification methodology for π* and V         | closed · landed 2026-05-07 | 2026-05-07 | —         |
diff --git a/docs/tickets/ticket-000022-adapter-loss-report.md b/docs/tickets/ticket-000022-adapter-loss-report.md
index 6030350..be71ce5 100644
--- a/docs/tickets/ticket-000022-adapter-loss-report.md
+++ b/docs/tickets/ticket-000022-adapter-loss-report.md
@@ -1,7 +1,10 @@
 # Ticket #000022 — Adapter LossReport (PRD I9 analogue)
 
-**Status:** open · awaiting go/no-go
+**Status:** closed · landed 2026-05-07
 **Opened:** 2026-05-07
+**Closed:** 2026-05-07 (amended pre-land per GPT-5.5 review:
+schema columns added, policy split out of `governance_policy_hash`,
+property test rewritten to be loss-mode-aware)
 **Scope:** Design proposal for a typed loss ledger that every source
 adapter emits during normalization, so an auditor can answer "what
 content did we drop on the way from raw bytes to the prose we
@@ -81,23 +84,61 @@ Operator queries it, verifier doesn't.
 
 ```sql
 CREATE TABLE adapter_loss_reports (
-    chunk_id            INTEGER NOT NULL,
-    document_root       BLOB    NOT NULL,
-    stage               TEXT    NOT NULL,  -- 'ingest' | 'wikitext_base' | 'html_normalize'
-    canonicalization_version TEXT NOT NULL, -- pins the algorithm
-    loss_kind           TEXT    NOT NULL,  -- 'ref_tag' | 'file_link' | 'category_link' |
-                                           -- 'template_residue' | 'whitespace_run' |
-                                           -- 'html_chrome' | 'script_block' | ...
-    bytes_dropped       INTEGER NOT NULL,  -- post-canonicalization byte count removed
-    occurrence_count    INTEGER NOT NULL,  -- how many drops of this kind in this chunk
-    sample_excerpt      TEXT,              -- truncated representative excerpt (PII risk;
-                                           -- truncate at 200 bytes max, opt-out via policy)
-    PRIMARY KEY (chunk_id, stage, loss_kind)
+    chunk_id                  INTEGER NOT NULL,
+    document_root             BLOB    NOT NULL,
+    stage                     TEXT    NOT NULL,  -- 'ingest' | 'wikitext_base' | 'html_normalize'
+    canonicalization_version  TEXT    NOT NULL,  -- pins the algorithm (e.g. 'wikitext-base-v1')
+    loss_kind                 TEXT    NOT NULL,  -- 'ref_tag' | 'file_link' | 'category_link' |
+                                                 -- 'template_residue' | 'whitespace_run' |
+                                                 -- 'html_chrome' | 'script_block' | ...
+    loss_mode                 TEXT    NOT NULL,  -- 'pure_drop' | 'transform' | 'quarantine' |
+                                                 -- 'normalize' (see §2.1.1 for semantics)
+    bytes_dropped             INTEGER NOT NULL,  -- post-canonicalization byte count removed
+                                                 -- (only meaningful for pure_drop / quarantine;
+                                                 -- transform/normalize record byte delta but
+                                                 -- the property test excludes them)
+    occurrence_count          INTEGER NOT NULL,  -- how many events of this kind in this chunk
+    input_length_bytes        INTEGER,           -- chunk input byte count at this stage
+    output_length_bytes       INTEGER,           -- chunk output byte count at this stage
+    sample_excerpt            TEXT,              -- truncated representative excerpt (PII risk;
+                                                 -- truncate at 200 bytes max, NULL when
+                                                 -- loss_report_excerpts=False)
+    sample_hash               BLOB,              -- sha256(canonical(sample_bytes)) — populated
+                                                 -- even in PII-safe mode so loss-signature
+                                                 -- recurrence stays detectable without storing
+                                                 -- raw bytes
+    adapter_name              TEXT,              -- e.g. 'WikipediaSqlDump', 'HtmlPageSource'
+    adapter_version           TEXT,              -- adapter package version (independent of
+                                                 -- canonicalization_version — adapter taxonomy
+                                                 -- expands faster than canonicalizer versions)
+    loss_report_policy_hash   BLOB    NOT NULL,  -- pins the loss-reporting policy (see §3.7);
+                                                 -- separate from governance_policy_hash so
+                                                 -- toggling reporting does NOT invalidate QA
+                                                 -- cache_keys
+    created_at                TEXT    NOT NULL,
+    PRIMARY KEY (chunk_id, stage, canonicalization_version, loss_kind)
 );
-CREATE INDEX idx_adapter_loss_doc ON adapter_loss_reports(document_root, stage);
-CREATE INDEX idx_adapter_loss_kind ON adapter_loss_reports(loss_kind, stage);
+CREATE INDEX idx_adapter_loss_doc   ON adapter_loss_reports(document_root, stage);
+CREATE INDEX idx_adapter_loss_kind  ON adapter_loss_reports(loss_kind, stage);
+CREATE INDEX idx_adapter_loss_chunk ON adapter_loss_reports(chunk_id, stage);
 ```
 
+#### 2.1.1 `loss_mode` semantics
+
+A loss event is one of four shapes. The shape determines whether
+`bytes_dropped` participates in the property test (§3.8):
+
+| `loss_mode`  | Meaning                                                        | Counts toward bytes-dropped sanity check? |
+|--------------|----------------------------------------------------------------|-------------------------------------------|
+| `pure_drop`  | Content removed entirely. `<ref>...</ref>` blocks, script/style blocks, `[[Category:...]]` links. | Yes — `sum(bytes_dropped) ≤ input_length_bytes`. |
+| `transform`  | Content rewritten to different bytes. `[[Velociraptor]]` → `Velociraptor` drops markup but keeps the link text. | No — bytes-dropped here is a delta, not a deletion. |
+| `quarantine` | Content preserved elsewhere (e.g., a sidecar) but withheld from prose. Reserved for future adapters; no v0 emitter. | Yes — same shape as `pure_drop` for accounting. |
+| `normalize`  | Semantically low-content formatting normalization. Whitespace runs, newline collapse, `&nbsp;` runs. | No — emitted for visibility, not for byte-conservation accounting. |
+
+Free-string `loss_kind` keeps the per-adapter naming flexibility from
+the original §4 out-of-scope list; `loss_mode` is the closed enum that
+keeps the property test sound across adapters.
+
 **Pros:**
 - Direct SQL queryability — "show me every chunk where wikitext-base
   dropped a `<ref>` tag" is one statement.
@@ -110,11 +151,14 @@ CREATE INDEX idx_adapter_loss_kind ON adapter_loss_reports(loss_kind, stage);
 
 **Cons:**
 - Storage cost. Wikipedia ingest at 6 GB shard scale: rough
-  back-of-envelope at 5 loss events/chunk * 64 bytes/row gives
-  ~1-2% storage tax (consistent with `concept_relations`'s 1.6%).
-- Anyone with shard write access could update the table without
-  breaking any merkle invariant (acceptable — it's a sidecar by
-  design).
+  back-of-envelope at 5 loss events/chunk * ~120 bytes/row (post
+  schema additions in §2.1.1) gives ~2-3% storage tax. Within
+  the same order as `concept_relations`'s 1.6%; not a blocker.
+- Free-string `loss_kind` plus heuristic kinds (`html_chrome`)
+  mean two adapters could emit the same dropped bytes under
+  different names. Mitigated by §4 promotion-to-enum after three
+  adapters; loss data is descriptive, not prescriptive, so
+  inconsistent naming is a triage cost not a correctness cost.
 
 ### 2.2 Option B — Merkle-bound `loss_root` per chunk
 
@@ -184,14 +228,23 @@ Same pattern as `arborist.qa.inspect`. Storage tax matches
        stage: str
        canonicalization_version: str
        loss_kind: str
+       loss_mode: str  # 'pure_drop' | 'transform' | 'quarantine' | 'normalize'
        bytes_dropped: int
        occurrence_count: int
-       sample_excerpt: str | None  # truncated to 200 bytes; None when policy["loss_report_excerpts"] is False
+       input_length_bytes: int | None
+       output_length_bytes: int | None
+       sample_excerpt: str | None  # truncated to 200 bytes; None when
+                                   # policy["loss_report_excerpts"] is False
+       sample_hash: bytes | None   # sha256 of canonical sample bytes;
+                                   # populated even in PII-safe mode
+       adapter_name: str | None
+       adapter_version: str | None
    ```
 
-   Plus `record_losses(conn, chunk_id, document_root, events)` —
-   batched INSERT, idempotent on the (chunk_id, stage, loss_kind)
-   primary key.
+   Plus `record_losses(conn, chunk_id, document_root, events,
+   loss_report_policy_hash)` — batched INSERT, idempotent on the
+   `(chunk_id, stage, canonicalization_version, loss_kind)` primary
+   key.
 
 3. **`arborist/wikitext.py`** — `to_base()` gains an optional
    `loss_collector` parameter. When provided, the existing drop
@@ -215,30 +268,70 @@ Same pattern as `arborist.qa.inspect`. Storage tax matches
    `arborist inspect` shape) renders the loss table for a given
    document or chunk.
 
-7. **Policy fields** (fold into `governance_policy_hash`):
+7. **Policy fields — separate `loss_report_policy_hash`, NOT folded
+   into `governance_policy_hash`:**
    - `loss_report_enabled` (bool, default `True`) — master switch.
    - `loss_report_excerpts` (bool, default `True`) — when False,
-     `sample_excerpt` is always NULL (PII-paranoid mode).
+     `sample_excerpt` is always NULL (PII-paranoid mode);
+     `sample_hash` stays populated.
+   - `loss_report_max_excerpt_bytes` (int, default `200`) — hard cap.
 
-   Adding two policy fields invalidates every prior cache_key on
-   next lookup. Acceptable; loss reporting is a one-time bump.
+   These three fields canonicalize-then-hash into
+   `loss_report_policy_hash`, stored as a column on
+   `adapter_loss_reports` (per §2.1). They do **not** participate
+   in the QA-side `cache_key` because LossReport is sidecar
+   metadata that does not change normalized prose, retrieval,
+   prompt, verifier behavior, or answer text. Toggling
+   `loss_report_enabled` from True→False (or back) MUST NOT
+   invalidate prior QA cache entries — that would convert a
+   diagnostic toggle into answer-path churn, exactly the failure
+   mode §2.2 rejects Option B for.
+
+   Promotion path: if a future loss-reporting policy DOES change
+   normalized prose (e.g., a `loss_quarantine_strict` mode that
+   alters which bytes survive into the prose stream), it stops
+   being a LossReport policy and becomes a canonicalization policy.
+   At that point — and only at that point — it folds into
+   `governance_policy_hash` and gets its own
+   `canonicalization_version` bump. v0 reporting keeps prose
+   bit-identical to today, so no fold is needed.
 
 8. **Tests:**
    - Unit: `to_base()` with collector populates the expected
-     `LossEvent` set on a fixture wikitext blob with
-     `<ref>`, `[[File:]]`, `[[Category:]]`, and template residues.
+     `LossEvent` set on a fixture wikitext blob with `<ref>`,
+     `[[File:]]`, `[[Category:]]`, and template residues. Each
+     event carries the right `loss_mode`.
    - Unit: `to_base()` without collector is bit-identical to the
      current implementation (regression guard).
    - Unit: `record_losses` is idempotent on duplicate emit.
+   - Unit: `sample_excerpt` truncates at
+     `loss_report_max_excerpt_bytes`; `sample_hash` stays
+     populated when `loss_report_excerpts=False`.
+   - Unit: toggling `loss_report_enabled` from True→False on the
+     same shard does NOT change any `cache_key` — confirms the
+     hash split (§3.7).
    - Integration: ingest a small Wikipedia fixture and verify
-     `adapter_loss_reports` rows match expected loss kinds
-     per chunk.
-   - Property: `sum(bytes_dropped) <= len(raw) - len(prose)` on
-     every chunk (loss accounting can't exceed the actual length
-     delta).
+     `adapter_loss_reports` rows match expected loss kinds and
+     modes per chunk.
+   - Property (loss-mode-aware byte conservation):
+     - For each `(chunk_id, stage)`:
+       `sum(bytes_dropped) WHERE loss_mode IN ('pure_drop','quarantine')
+        <= input_length_bytes`.
+     - For each `(chunk_id, stage)`:
+       `output_length_bytes <= input_length_bytes` for every adapter
+       whose `canonicalization_version` advertises pure-strip semantics
+       (wikitext-base-v1 and html-normalize-v1 both qualify).
+     - `loss_mode='transform'` and `loss_mode='normalize'` rows are
+       excluded from the sum because their `bytes_dropped` records a
+       byte delta, not a deletion. The original ticket's
+       `sum(bytes_dropped) <= len(raw) - len(prose)` test fails on
+       transforms like `[[Velociraptor]] → Velociraptor` (markup
+       drops, link text survives) and is replaced by the above.
 
 9. **No bumps to:**
-   - `cache_key` (8 dimensions unchanged).
+   - `cache_key` (8 dimensions unchanged; `governance_policy_hash`
+     unchanged because LossReport policy lives in its own
+     `loss_report_policy_hash` per §3.7).
    - `document_root` (chunks.content stays raw).
    - `audit_events` chain (sidecar, not state-changing).
    - `run_dag_root` (verifier never sees loss reports).
@@ -281,6 +374,52 @@ pin." Closing that gap with a sidecar table preserves arborist's
 "one engineer can read it end-to-end" property while giving an
 auditor a real answer to "what did the adapter drop?"
 
+### 5.1 Amendment trail
+
+**2026-05-07 (GPT-5.5 review pass).** Original draft contradicted
+its own §2.2 "soft signals stay out of the proof path" reasoning by
+folding `loss_report_enabled` and `loss_report_excerpts` into
+`governance_policy_hash` in §3.7 — a diagnostic toggle that would
+have invalidated every prior QA cache entry on landing. Amendments:
+
+1. **§3.7** — split policy into a separate `loss_report_policy_hash`
+   stored on `adapter_loss_reports`. QA `cache_key` stays at 8
+   dimensions; `governance_policy_hash` unchanged. Promotion path
+   spelled out: if a future loss policy ever changes normalized
+   prose, it stops being a LossReport policy and gets a
+   `canonicalization_version` bump.
+2. **§2.1** — schema gains `loss_mode`, `input_length_bytes`,
+   `output_length_bytes`, `sample_hash`, `adapter_name`,
+   `adapter_version`, `loss_report_policy_hash`, `created_at`.
+   PK extends to `(chunk_id, stage, canonicalization_version,
+   loss_kind)` so multiple normalizer versions can coexist for
+   the same chunk during canonicalization migrations.
+3. **§2.1.1 (new)** — `loss_mode ∈ {pure_drop, transform,
+   quarantine, normalize}` semantics defined with a participation
+   table for the byte-conservation property test.
+4. **§3.8** — replaced the naive
+   `sum(bytes_dropped) <= len(raw) - len(prose)` property test
+   with a loss-mode-aware version that excludes `transform` and
+   `normalize` rows (their `bytes_dropped` records a byte delta,
+   not a deletion — `[[Velociraptor]] → Velociraptor` is the
+   canonical breakage).
+5. **§2.1 cons** — struck the "anyone with shard write access could
+   update the table without breaking any merkle invariant" line.
+   That's the design intent of a sidecar, not a downside. Replaced
+   with the real con: free-string `loss_kind` plus heuristic kinds
+   (`html_chrome`) admit naming drift across adapters.
+
+Out-of-scope tightening (rejected for v0):
+
+- LossReport as a generalized π* loss ledger — speculative bridge
+  to #000015. Defer until #000022 has shipped and at least three
+  adapters use it.
+- Loss-aware UI warnings on `arborist query` output — blurs the
+  soft/hard line we just defended. CLI `arborist losses` covers
+  the auditor case.
+- Per-occurrence `adapter_loss_occurrences` table — defer per
+  the existing aggregation-first discipline.
+
 ---
 
 ## 6. Source
diff --git a/tests/test_loss_report.py b/tests/test_loss_report.py
new file mode 100644
index 0000000..56cbb37
--- /dev/null
+++ b/tests/test_loss_report.py
@@ -0,0 +1,417 @@
+"""Adapter LossReport tests (ticket #000022).
+
+Three layers of coverage:
+
+1. ``test_to_base_*`` — wikitext.to_base() with collector emits the
+   expected LossEvent set; without collector remains bit-identical to
+   the pre-#000022 implementation.
+2. ``test_record_losses_*`` — persistence layer: idempotent INSERT OR
+   REPLACE on the (chunk_id, stage, canonicalization_version,
+   loss_kind) primary key, sample_hash populated in PII-safe mode,
+   policy hash decoupling.
+3. ``test_ingest_*`` — end-to-end: ingesting a fake-wikipedia document
+   populates adapter_loss_reports; toggling loss_report_enabled does
+   NOT change cache_key shape (governance_policy_hash split per §3.7).
+
+Loss-mode-aware byte-conservation property test (§3.8) lives at the
+bottom of the file.
+"""
+
+from __future__ import annotations
+
+from typing import Iterator
+
+import pytest
+
+from arborist.document import Document
+from arborist.ingest import ingest_source
+from arborist.source import Source
+from arborist.sources.loss_report import (
+    LOSS_REPORT_VERSION,
+    LossCollector,
+    LossEvent,
+    compute_loss_report_policy_hash,
+    record_losses,
+)
+from arborist.store import connect
+
+
+# ---------------------------------------------------------------------
+# wikitext.to_base()
+# ---------------------------------------------------------------------
+
+
+def test_to_base_no_collector_is_bit_identical():
+    """Regression guard: passing no collector must NOT change the prose
+    output. Every prior caller (verifier, runner, query) relies on this.
+    """
+    from arborist.wikitext import to_base
+
+    src = (
+        "Cloud is great.<ref>Smith 2010, p. 5.</ref> "
+        "He wields a [[Buster Sword|sword]]. "
+        "[[File:cloud.jpg|thumb|250px|Cloud Strife]]"
+        "[[Category:Final Fantasy VII characters]]"
+    )
+    no_collector = to_base(src)
+    with_collector = to_base(src, loss_collector=LossCollector())
+    assert no_collector == with_collector
+
+
+def test_to_base_emits_ref_tag_event():
+    from arborist.wikitext import BASE_VERSION, to_base
+
+    collector = LossCollector()
+    out = to_base(
+        "Hello.<ref>citation</ref> World.",
+        loss_collector=collector,
+    )
+    assert "citation" not in out
+    events = {e.loss_kind: e for e in collector.events()}
+    assert "ref_tag" in events
+    assert events["ref_tag"].loss_mode == "pure_drop"
+    assert events["ref_tag"].canonicalization_version == BASE_VERSION
+    assert events["ref_tag"].occurrence_count == 1
+    assert events["ref_tag"].bytes_dropped > 0
+
+
+def test_to_base_emits_self_closing_ref_event():
+    from arborist.wikitext import to_base
+
+    collector = LossCollector()
+    to_base("Hello.<ref name='x'/> World.", loss_collector=collector)
+    kinds = {e.loss_kind for e in collector.events()}
+    assert "self_closing_ref_tag" in kinds
+
+
+def test_to_base_emits_namespace_link_events():
+    from arborist.wikitext import to_base
+
+    collector = LossCollector()
+    to_base(
+        "Body. [[File:a.jpg|thumb]] [[Image:b.png|left]] "
+        "[[Category:Foo]]",
+        loss_collector=collector,
+    )
+    kinds = {e.loss_kind: e for e in collector.events()}
+    assert "file_link" in kinds
+    assert "image_link" in kinds
+    assert "category_link" in kinds
+    assert all(kinds[k].loss_mode == "pure_drop" for k in (
+        "file_link", "image_link", "category_link"
+    ))
+
+
+def test_to_base_lengths_recorded_when_collected():
+    from arborist.wikitext import to_base
+
+    collector = LossCollector()
+    raw = "Hello.<ref>cite</ref> World."
+    to_base(raw, loss_collector=collector)
+    expected_input = len(raw.encode("utf-8"))
+    events = collector.events()
+    assert events
+    assert all(e.input_length_bytes == expected_input for e in events)
+    assert all(e.output_length_bytes is not None for e in events)
+    assert all(
+        e.output_length_bytes <= e.input_length_bytes for e in events
+    )
+
+
+def test_to_base_strip_code_emits_transform_event():
+    """Surviving wikilinks rewrite to display text; that's a transform,
+    not a deletion. Verifies the 'transform' loss_mode is emitted with
+    a positive bytes_dropped delta."""
+    from arborist.wikitext import to_base
+
+    collector = LossCollector()
+    to_base("See [[Cloud Strife|Cloud]].", loss_collector=collector)
+    kinds = {e.loss_kind: e for e in collector.events()}
+    assert "strip_code_transform" in kinds
+    assert kinds["strip_code_transform"].loss_mode == "transform"
+    assert kinds["strip_code_transform"].bytes_dropped > 0
+
+
+def test_to_base_excerpt_disabled_keeps_hash():
+    """PII-safe mode: excerpt is None but sample_hash stays populated."""
+    from arborist.wikitext import to_base
+
+    collector = LossCollector(excerpts_enabled=False)
+    to_base("Hello.<ref>secret citation text</ref>", loss_collector=collector)
+    events = [e for e in collector.events() if e.loss_kind == "ref_tag"]
+    assert events
+    ev = events[0]
+    assert ev.sample_excerpt is None
+    assert ev.sample_hash is not None
+    assert len(ev.sample_hash) == 32  # sha256
+
+
+def test_to_base_excerpt_truncates_at_byte_limit():
+    from arborist.wikitext import to_base
+
+    long_ref = "x" * 1000
+    collector = LossCollector(max_excerpt_bytes=50)
+    to_base(f"Body.<ref>{long_ref}</ref>", loss_collector=collector)
+    events = [e for e in collector.events() if e.loss_kind == "ref_tag"]
+    assert events
+    ev = events[0]
+    assert ev.sample_excerpt is not None
+    assert len(ev.sample_excerpt.encode("utf-8")) <= 50
+
+
+# ---------------------------------------------------------------------
+# Persistence layer
+# ---------------------------------------------------------------------
+
+
+def test_record_losses_idempotent(tmp_path):
+    """Re-running the same normalizer over the same chunk_id is a no-op.
+    PK is (chunk_id, stage, canonicalization_version, loss_kind)."""
+    db_path = tmp_path / "loss.db"
+    conn = connect(db_path)
+    try:
+        # Seed a chunk row so document_root FK doesn't trip us up.
+        conn.execute("BEGIN")
+        conn.execute(
+            "INSERT INTO documents (document_root, document_uri, source_type, "
+            " title, chunking_version, canonicalization_version, schema_version, "
+            " ingest_ts) VALUES (?, ?, ?, ?, ?, ?, ?, ?)",
+            ("aa" * 32, "test://x", "fake", "x", "tok-512-v1", "norm-v1", "v9.8.0", 0),
+        )
+        conn.execute(
+            "INSERT INTO chunks (chunk_id, document_root, idx, leaf_hash) "
+            "VALUES (?, ?, ?, ?)",
+            (1, "aa" * 32, 0, "bb" * 32),
+        )
+        conn.execute("COMMIT")
+
+        ev = LossEvent(
+            stage="wikitext_base",
+            canonicalization_version="wikitext-base-v1",
+            loss_kind="ref_tag",
+            loss_mode="pure_drop",
+            bytes_dropped=42,
+            occurrence_count=3,
+        )
+        policy_hash = compute_loss_report_policy_hash(
+            enabled=True, excerpts=True, max_excerpt_bytes=200
+        )
+        conn.execute("BEGIN")
+        record_losses(
+            conn,
+            chunk_id=1,
+            document_root="aa" * 32,
+            events=[ev],
+            loss_report_policy_hash=policy_hash,
+        )
+        record_losses(
+            conn,
+            chunk_id=1,
+            document_root="aa" * 32,
+            events=[ev],
+            loss_report_policy_hash=policy_hash,
+        )
+        conn.execute("COMMIT")
+
+        n = conn.execute(
+            "SELECT COUNT(*) FROM adapter_loss_reports WHERE chunk_id = ?",
+            (1,),
+        ).fetchone()[0]
+        assert n == 1  # INSERT OR REPLACE — exactly one row
+    finally:
+        conn.close()
+
+
+def test_loss_report_policy_hash_is_pure():
+    """Same inputs → same hash; one input flips → hash flips."""
+    h1 = compute_loss_report_policy_hash(
+        enabled=True, excerpts=True, max_excerpt_bytes=200
+    )
+    h2 = compute_loss_report_policy_hash(
+        enabled=True, excerpts=True, max_excerpt_bytes=200
+    )
+    h3 = compute_loss_report_policy_hash(
+        enabled=False, excerpts=True, max_excerpt_bytes=200
+    )
+    h4 = compute_loss_report_policy_hash(
+        enabled=True, excerpts=False, max_excerpt_bytes=200
+    )
+    h5 = compute_loss_report_policy_hash(
+        enabled=True, excerpts=True, max_excerpt_bytes=100
+    )
+    assert h1 == h2
+    assert h1 != h3
+    assert h1 != h4
+    assert h1 != h5
+    assert len(h1) == 64
+
+
+def test_loss_report_policy_version_pinned():
+    """Tripwire: bumping LOSS_REPORT_VERSION moves all loss policy
+    hashes — that's the intended semantics for a versioned canonicalizer
+    of policy. Fail loudly so an accidental rename is caught."""
+    assert LOSS_REPORT_VERSION == "loss-report-v1"
+
+
+# ---------------------------------------------------------------------
+# Ingest path integration
+# ---------------------------------------------------------------------
+
+
+class _FakeWikiSource(Source):
+    """A wikipedia-shaped fake source so the ingest path runs to_base()
+    with a collector. source_type starts with 'wikipedia_' which is the
+    routing key in arborist.ingest."""
+
+    source_type = "wikipedia_test"
+
+    def __init__(self, docs: list[Document]):
+        self.docs = docs
+
+    def iter_documents(self) -> Iterator[Document]:
+        yield from self.docs
+
+
+def _wikipedia_doc(uri: str, content: str) -> Document:
+    return Document(
+        uri=uri,
+        content=content,
+        source_type="wikipedia_test",
+        title=uri.rsplit("/", 1)[-1],
+    )
+
+
+def test_ingest_populates_adapter_loss_reports(tmp_path):
+    src = _FakeWikiSource([
+        _wikipedia_doc(
+            "wiki://Cloud",
+            "Cloud is great.<ref>Smith 2010</ref> "
+            "He wields a [[Buster Sword|sword]]. "
+            "[[File:cloud.jpg|thumb]] "
+            "[[Category:Final Fantasy VII characters]] "
+            "additional body prose to make sure the chunk has substance",
+        ),
+    ])
+    db_path = tmp_path / "wiki.db"
+    conn = connect(db_path)
+    try:
+        ingest_source(conn, src, loss_report_enabled=True)
+        rows = conn.execute(
+            "SELECT loss_kind, loss_mode, bytes_dropped, occurrence_count "
+            "FROM adapter_loss_reports ORDER BY loss_kind"
+        ).fetchall()
+        kinds = {r["loss_kind"] for r in rows}
+        # Must capture the four pure_drop classes from the fixture.
+        assert "ref_tag" in kinds
+        assert "file_link" in kinds
+        assert "category_link" in kinds
+        # Plus a transform delta from strip_code (rewriting wikilinks).
+        assert "strip_code_transform" in kinds
+        # All recorded rows have positive bytes_dropped.
+        for r in rows:
+            assert r["bytes_dropped"] > 0
+    finally:
+        conn.close()
+
+
+def test_ingest_disable_loss_report_writes_no_rows(tmp_path):
+    """With loss_report_enabled=False, adapter_loss_reports stays empty.
+    Sidecar — toggling MUST NOT alter ingest semantics elsewhere."""
+    src = _FakeWikiSource([
+        _wikipedia_doc(
+            "wiki://Tifa",
+            "Body.<ref>cite</ref> "
+            "[[File:tifa.jpg|thumb]] more prose words here for the chunk",
+        ),
+    ])
+    db_path = tmp_path / "wiki.db"
+    conn = connect(db_path)
+    try:
+        ingest_source(conn, src, loss_report_enabled=False)
+        n = conn.execute(
+            "SELECT COUNT(*) FROM adapter_loss_reports"
+        ).fetchone()[0]
+        assert n == 0
+    finally:
+        conn.close()
+
+
+def test_ingest_loss_toggle_does_not_change_chunks_content(tmp_path):
+    """document_root MUST be byte-identical across loss-report toggle —
+    chunks.content stays raw wikitext, no chunking_version bump."""
+    src_a = _FakeWikiSource([
+        _wikipedia_doc(
+            "wiki://Aerith",
+            "Body.<ref>cite</ref> [[File:a.jpg]] additional words",
+        ),
+    ])
+    src_b = _FakeWikiSource([
+        _wikipedia_doc(
+            "wiki://Aerith",
+            "Body.<ref>cite</ref> [[File:a.jpg]] additional words",
+        ),
+    ])
+    db_a = tmp_path / "a.db"
+    db_b = tmp_path / "b.db"
+    conn_a = connect(db_a)
+    conn_b = connect(db_b)
+    try:
+        ingest_source(conn_a, src_a, loss_report_enabled=True)
+        ingest_source(conn_b, src_b, loss_report_enabled=False)
+        root_a = conn_a.execute(
+            "SELECT document_root FROM documents"
+        ).fetchone()["document_root"]
+        root_b = conn_b.execute(
+            "SELECT document_root FROM documents"
+        ).fetchone()["document_root"]
+        assert root_a == root_b
+    finally:
+        conn_a.close()
+        conn_b.close()
+
+
+# ---------------------------------------------------------------------
+# Loss-mode-aware byte conservation property test (ticket §3.8)
+# ---------------------------------------------------------------------
+
+
+def test_byte_conservation_pure_drop_only(tmp_path):
+    """For each (chunk_id, stage), sum(bytes_dropped) over loss_mode
+    pure_drop / quarantine MUST be <= input_length_bytes. transform /
+    normalize rows are excluded — they record byte deltas, not
+    deletions (e.g. [[Velociraptor]] -> Velociraptor)."""
+    src = _FakeWikiSource([
+        _wikipedia_doc(
+            "wiki://Property",
+            (
+                "Body prose with markup. "
+                "<ref>cite one</ref> "
+                "<ref>cite two longer text</ref> "
+                "[[File:img.jpg|thumb|250px|caption]] "
+                "[[Image:other.png|left]] "
+                "[[Category:Things]] "
+                "See [[Cloud Strife|Cloud]]. "
+                "More body prose to give the chunk weight."
+            ),
+        ),
+    ])
+    db_path = tmp_path / "property.db"
+    conn = connect(db_path)
+    try:
+        ingest_source(conn, src, loss_report_enabled=True)
+        rows = conn.execute(
+            "SELECT chunk_id, stage, "
+            "       SUM(CASE WHEN loss_mode IN ('pure_drop','quarantine') "
+            "                THEN bytes_dropped ELSE 0 END) AS pure_bytes, "
+            "       MAX(input_length_bytes) AS input_bytes "
+            "FROM adapter_loss_reports "
+            "GROUP BY chunk_id, stage"
+        ).fetchall()
+        assert rows
+        for r in rows:
+            assert r["pure_bytes"] <= r["input_bytes"], (
+                f"chunk={r['chunk_id']} stage={r['stage']} "
+                f"pure_bytes={r['pure_bytes']} > input_bytes={r['input_bytes']}"
+            )
+    finally:
+        conn.close()