attest: drop v2 schema bump — no v1 records exist, cites is just a v1 field

The v1→v2 bump in 30aba0e was ceremony with no historical witnesses.
A sweep of every local SQLite (~/.arborist/shards/*.db,
~/.arborist/*.db) found zero ``attest_fingerprint`` audit rows; the
module was introduced on this branch with no commits outside test
fixtures. With no v1 bodies in the wild there is no canonical-bytes
divergence to mark — v2 is just better v1.

- ``SCHEMA_VERSION`` returns to ``fingerprint-v1``.
- ``cites: tuple[str, ...] = ()`` stays on the dataclass; it was the
  actual feature, not the version bump.
- ``entity_chain_iter`` reads ``body["cites"]`` directly — no
  ``.get(..., ())`` defensive fallback for a missing-field case that
  cannot arise.
- ``test_legacy_v1_body_without_cites_reconstructs_with_empty_tuple``
  removed — it tested a backwards-compat path with no caller.
- ``blast_radius`` unchanged.

Net: -31 lines of compat scaffolding for a population of zero
records. Per CLAUDE.md "don't add backwards-compatibility shims when
you can just change the code" and the five-step algorithm step 2
("delete the part"). 66 attest tests pass.

arborist/attest/chain.py

@@ -154,7 +154,7 @@ def entity_chain_iter(
             skew_q10000=int(body["skew_q10000"]),
             error_taxonomy={k: int(v) for k, v in body.get("error_taxonomy", {}).items()},
             stress_params={k: int(v) for k, v in body.get("stress_params", {}).items()},
-            cites=tuple(body.get("cites", ())),
+            cites=tuple(body["cites"]),
             schema_version=body["schema_version"],
         )
         yield n, event_hash, fp

arborist/attest/fingerprint.py

@@ -1,6 +1,6 @@
 """Fingerprint schema + canonical encoder + Merkle leaf hash.
 
-Schema version: ``fingerprint-v2``.
+Schema version: ``fingerprint-v1``.
 
 All numeric fields are integers. Latency lives in microseconds.
 Skew is quantized to a 4-decimal-place integer (``skew_q10000``).
@@ -14,15 +14,13 @@ by ±1 in the last digit of ``skew_q10000`` or one of the std/mean
 fields. Acceptable for v1; a future revision can compute moments in
 integer arithmetic if required.
 
-**v2 delta: optional ``cites`` field.** A fingerprint may declare a
-``cites`` tuple of other entities' chain hashes that it vouches for
-or depends on. The citation is a *claim of dependency*, not a
-verification — at commit time arborist does not re-verify the cited
-chain. The point is that if a cited chain hash is later falsified
-(KS / Mahalanobis drift, manual quarantine, etc.), the audit graph
-yields a deterministic blast radius via ``chain.blast_radius()``.
-Default empty tuple → equivalent to v1 semantics. Legacy v1 bodies
-in storage (no ``cites`` key) are reconstructed with ``cites=()``.
+**``cites`` field.** A fingerprint may declare a ``cites`` tuple of
+other entities' chain hashes that it vouches for or depends on. The
+citation is a *claim of dependency*, not a verification — at commit
+time arborist does not re-verify the cited chain. The point is that
+if a cited chain hash is later falsified (KS / Mahalanobis drift,
+manual quarantine, etc.), the audit graph yields a deterministic
+blast radius via ``chain.blast_radius()``. Default empty tuple.
 """
 
 from __future__ import annotations
@@ -35,7 +33,7 @@ from typing import Mapping, Sequence
 
 from arborist.merkle import hash_leaf
 
-SCHEMA_VERSION = "fingerprint-v2"
+SCHEMA_VERSION = "fingerprint-v1"
 
 
 @dataclass(frozen=True)

tests/test_attest_chain.py

@@ -240,32 +240,3 @@ def test_blast_radius_misses_unrelated_chain_hash(tmp_path):
     )
     assert blast_radius(conn, "f" * 64) == []
 
-
-def test_legacy_v1_body_without_cites_reconstructs_with_empty_tuple(tmp_path):
-    """v1 events in storage (no `cites` key) must round-trip through entity_chain_iter."""
-    from arborist.store import append_audit
-
-    conn = connect(tmp_path / "t.db")
-    legacy_body = {
-        "entity_id": "alice",
-        "session_id": "s-legacy",
-        "timestamp_utc": "2026-06-05T15:30:00Z",
-        "domain": "python-debug",
-        "host_hash": "0" * 64,
-        "count": 3,
-        "mean_us": 1000,
-        "std_us": 100,
-        "p50_us": 1000,
-        "p90_us": 1100,
-        "p99_us": 1200,
-        "skew_q10000": 0,
-        "error_taxonomy": {},
-        "stress_params": {},
-        "schema_version": "fingerprint-v1",
-    }
-    append_audit(conn, event_type=EVENT_TYPE, body=legacy_body, subject_root="alice")
-    seen = list(entity_chain_iter(conn, "alice"))
-    assert len(seen) == 1
-    fp = seen[0][2]
-    assert fp.cites == ()
-    assert fp.schema_version == "fingerprint-v1"