diff --git a/Makefile b/Makefile
index 86aa3f4..73ea5f3 100644
--- a/Makefile
+++ b/Makefile
@@ -242,6 +242,22 @@ bench-emergent-pending: bootstrap ## print log entries awaiting teacher review
 	$(PY) scripts/bench_emergent.py --print-pending
 
 
+bench-5s: bootstrap ## 5S battery (Syntax + Semantics) on Phase-1a seed fixtures
+	PYTHONUNBUFFERED=1 $(PY) -m bench.batteries.runner \
+	    --battery 5s --sub syntax \
+	    --fixtures bench/fixtures/5s/syntax-v1.jsonl
+	PYTHONUNBUFFERED=1 $(PY) -m bench.batteries.runner \
+	    --battery 5s --sub semantics \
+	    --fixtures bench/fixtures/5s/semantics-v1.jsonl
+
+bench-5t: bootstrap ## 5T battery (Transfer) on Phase-1a seed fixture
+	PYTHONUNBUFFERED=1 $(PY) -m bench.batteries.runner \
+	    --battery 5t --sub transfer \
+	    --fixtures bench/fixtures/5t/transfer-v1.jsonl
+
+bench-5s5t: bench-5s bench-5t ## both Phase-1a batteries (alias)
+
+
 verify-shards: bootstrap ## cross-shard Merkle round-trip on a random sample
 	$(ARBORIST) --shards-dir $(SHARDS_DIR) verify -n $(VERIFY_N)
 
diff --git a/bench/batteries/__init__.py b/bench/batteries/__init__.py
new file mode 100644
index 0000000..52e7f9a
--- /dev/null
+++ b/bench/batteries/__init__.py
@@ -0,0 +1,13 @@
+"""5S/5T/5R battery harness (ticket #000021).
+
+Phase 1a (this landing): 5S Syntax + 5S Semantics + 5T Transfer
+runners with seed fixtures. Phase 1b (full fixture authoring) and
+Phase 2 (5R battery, depends on tickets #000014 + #000017) land
+in follow-up tickets.
+"""
+
+from __future__ import annotations
+
+from bench.batteries.base import Battery, BatteryResult, TaskResult
+
+__all__ = ["Battery", "BatteryResult", "TaskResult"]
diff --git a/bench/batteries/b_5s.py b/bench/batteries/b_5s.py
new file mode 100644
index 0000000..fb5a2a1
--- /dev/null
+++ b/bench/batteries/b_5s.py
@@ -0,0 +1,163 @@
+"""5S battery — Syntax / Semantics / Synthesis / Syllogism / Semiotics.
+
+Phase 1a implements Syntax and Semantics against arborist's π*
+registry. The other three sub-batteries are reserved as stubs that
+return zero-task BatteryResults; full fixtures + runners land in
+follow-up tickets.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from bench.batteries.base import (
+    BatteryResult,
+    TaskResult,
+    fixture_digest,
+    fixture_meta,
+    iter_tasks,
+)
+
+
+def _runtime_digest() -> str:
+    """SHA-256 fingerprint of the active π* registry.
+
+    Includes name@version of every registered π* so a registry change
+    surfaces in the runtime_digest.
+    """
+    import hashlib
+
+    from arborist.pi_star import list_keys
+
+    payload = "\n".join(list_keys()).encode("utf-8")
+    return hashlib.sha256(payload).hexdigest()
+
+
+def run_syntax(fixtures_path: Path) -> BatteryResult:
+    """Each task asserts that the named π* canonicalizes the input
+    without raising. expected="pass" is the only supported expected;
+    other values fail loudly."""
+    from arborist.pi_star import get
+
+    per_task: list[TaskResult] = []
+    pass_count = 0
+    fail_count = 0
+    for task in iter_tasks(fixtures_path):
+        task_id = task["id"]
+        ok = False
+        detail: dict = {}
+        try:
+            pi_star = get(task["pi_star"])
+            pi_star.canonicalize(task["input"].encode("utf-8"))
+            ok = task.get("expected", "pass") == "pass"
+            if not ok:
+                detail["reason"] = "canonicalize succeeded but expected != pass"
+        except NotImplementedError:
+            detail["reason"] = "pi_star is a stub"
+            ok = False
+        except Exception as exc:  # noqa: BLE001
+            detail["reason"] = f"{type(exc).__name__}: {exc}"
+            ok = False
+        if ok:
+            pass_count += 1
+        else:
+            fail_count += 1
+        per_task.append(TaskResult(task_id=task_id, passed=ok, detail=detail))
+
+    total = pass_count + fail_count
+    pass_rate = pass_count / total if total else 0.0
+    meta = fixture_meta(fixtures_path)
+    return BatteryResult(
+        battery="5s",
+        sub_battery=meta.get("sub_battery", "syntax"),
+        fixture_path=str(fixtures_path),
+        fixture_digest=fixture_digest(fixtures_path),
+        pass_count=pass_count,
+        fail_count=fail_count,
+        metrics={"parse_pass_rate": pass_rate},
+        per_task=per_task,
+        runtime_digest=_runtime_digest(),
+    )
+
+
+def run_semantics(fixtures_path: Path) -> BatteryResult:
+    """Each task: two inputs + a π*; passes if canonicalize agrees with
+    expected_equivalent."""
+    from arborist.pi_star import get
+
+    per_task: list[TaskResult] = []
+    pass_count = 0
+    fail_count = 0
+    for task in iter_tasks(fixtures_path):
+        task_id = task["id"]
+        ok = False
+        detail: dict = {}
+        try:
+            pi_star = get(task["pi_star"])
+            ca = pi_star.canonicalize(task["input_a"].encode("utf-8"))
+            cb = pi_star.canonicalize(task["input_b"].encode("utf-8"))
+            equivalent = ca == cb
+            ok = equivalent == bool(task["expected_equivalent"])
+            if not ok:
+                detail["reason"] = (
+                    f"observed_equivalent={equivalent} "
+                    f"expected={task['expected_equivalent']}"
+                )
+        except Exception as exc:  # noqa: BLE001
+            detail["reason"] = f"{type(exc).__name__}: {exc}"
+            ok = False
+        if ok:
+            pass_count += 1
+        else:
+            fail_count += 1
+        per_task.append(TaskResult(task_id=task_id, passed=ok, detail=detail))
+
+    total = pass_count + fail_count
+    rate = pass_count / total if total else 0.0
+    meta = fixture_meta(fixtures_path)
+    return BatteryResult(
+        battery="5s",
+        sub_battery=meta.get("sub_battery", "semantics"),
+        fixture_path=str(fixtures_path),
+        fixture_digest=fixture_digest(fixtures_path),
+        pass_count=pass_count,
+        fail_count=fail_count,
+        metrics={"equivalence_recovery_rate": rate},
+        per_task=per_task,
+        runtime_digest=_runtime_digest(),
+    )
+
+
+def _stub_result(name: str, fixtures_path: Path) -> BatteryResult:
+    return BatteryResult(
+        battery="5s",
+        sub_battery=name,
+        fixture_path=str(fixtures_path),
+        fixture_digest="",
+        pass_count=0,
+        fail_count=0,
+        metrics={},
+        per_task=[],
+        runtime_digest="",
+    )
+
+
+def run_synthesis(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("synthesis", fixtures_path)
+
+
+def run_syllogism(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("syllogism", fixtures_path)
+
+
+def run_semiotics(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("semiotics", fixtures_path)
+
+
+SUB_BATTERIES = {
+    "syntax": run_syntax,
+    "semantics": run_semantics,
+    "synthesis": run_synthesis,
+    "syllogism": run_syllogism,
+    "semiotics": run_semiotics,
+}
diff --git a/bench/batteries/b_5t.py b/bench/batteries/b_5t.py
new file mode 100644
index 0000000..14c81d0
--- /dev/null
+++ b/bench/batteries/b_5t.py
@@ -0,0 +1,105 @@
+"""5T battery — Transfer / Triangulate / Timing / Transitivity / Truth.
+
+Phase 1a implements Transfer (paraphrase-invariance under a π*).
+The other four sub-batteries are reserved as stubs.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from bench.batteries.base import (
+    BatteryResult,
+    TaskResult,
+    fixture_digest,
+    fixture_meta,
+    iter_tasks,
+)
+from bench.batteries.b_5s import _runtime_digest
+
+
+def run_transfer(fixtures_path: Path) -> BatteryResult:
+    """Each task: π* + two surface variants → does canonicalize
+    collapse them as expected_equivalent says it should?"""
+    from arborist.pi_star import get
+
+    per_task: list[TaskResult] = []
+    pass_count = 0
+    fail_count = 0
+    for task in iter_tasks(fixtures_path):
+        task_id = task["id"]
+        ok = False
+        detail: dict = {}
+        try:
+            pi_star = get(task["pi_star"])
+            ca = pi_star.canonicalize(task["input_a"].encode("utf-8"))
+            cb = pi_star.canonicalize(task["input_b"].encode("utf-8"))
+            equivalent = ca == cb
+            ok = equivalent == bool(task["expected_equivalent"])
+            if not ok:
+                detail["reason"] = (
+                    f"observed_equivalent={equivalent} "
+                    f"expected={task['expected_equivalent']}"
+                )
+        except Exception as exc:  # noqa: BLE001
+            detail["reason"] = f"{type(exc).__name__}: {exc}"
+            ok = False
+        if ok:
+            pass_count += 1
+        else:
+            fail_count += 1
+        per_task.append(TaskResult(task_id=task_id, passed=ok, detail=detail))
+
+    total = pass_count + fail_count
+    rate = pass_count / total if total else 0.0
+    meta = fixture_meta(fixtures_path)
+    return BatteryResult(
+        battery="5t",
+        sub_battery=meta.get("sub_battery", "transfer"),
+        fixture_path=str(fixtures_path),
+        fixture_digest=fixture_digest(fixtures_path),
+        pass_count=pass_count,
+        fail_count=fail_count,
+        metrics={"transfer_pass_rate": rate},
+        per_task=per_task,
+        runtime_digest=_runtime_digest(),
+    )
+
+
+def _stub_result(name: str, fixtures_path: Path) -> BatteryResult:
+    return BatteryResult(
+        battery="5t",
+        sub_battery=name,
+        fixture_path=str(fixtures_path),
+        fixture_digest="",
+        pass_count=0,
+        fail_count=0,
+        metrics={},
+        per_task=[],
+        runtime_digest="",
+    )
+
+
+def run_triangulate(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("triangulate", fixtures_path)
+
+
+def run_timing(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("timing", fixtures_path)
+
+
+def run_transitivity(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("transitivity", fixtures_path)
+
+
+def run_truth(fixtures_path: Path) -> BatteryResult:
+    return _stub_result("truth", fixtures_path)
+
+
+SUB_BATTERIES = {
+    "transfer": run_transfer,
+    "triangulate": run_triangulate,
+    "timing": run_timing,
+    "transitivity": run_transitivity,
+    "truth": run_truth,
+}
diff --git a/bench/batteries/base.py b/bench/batteries/base.py
new file mode 100644
index 0000000..1ab6579
--- /dev/null
+++ b/bench/batteries/base.py
@@ -0,0 +1,92 @@
+"""Battery base classes.
+
+A Battery runs a fixture file end-to-end against a specified runtime
+(usually arborist's existing surface) and emits a deterministic
+:class:`BatteryResult`. Determinism: same fixture digest + same code
+digest → identical result (modulo wall-clock fields).
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import time
+from dataclasses import asdict, dataclass, field
+from pathlib import Path
+from typing import Any, Iterable, Optional, Protocol
+
+
+@dataclass
+class TaskResult:
+    """Per-task outcome inside a battery run."""
+
+    task_id: str
+    passed: bool
+    detail: dict[str, Any] = field(default_factory=dict)
+
+
+@dataclass
+class BatteryResult:
+    """End-to-end battery result; deterministic given fixed inputs."""
+
+    battery: str
+    sub_battery: str
+    fixture_path: str
+    fixture_digest: str
+    pass_count: int
+    fail_count: int
+    metrics: dict[str, float] = field(default_factory=dict)
+    per_task: list[TaskResult] = field(default_factory=list)
+    runtime_digest: str = ""
+    timestamp: int = field(default_factory=lambda: int(time.time()))
+
+    def to_dict(self) -> dict:
+        d = asdict(self)
+        return d
+
+
+class Battery(Protocol):
+    """One sub-battery (e.g., 5S Syntax)."""
+
+    name: str
+
+    def run(self, fixtures_path: Path) -> BatteryResult:
+        ...
+
+
+def fixture_digest(fixtures_path: Path) -> str:
+    """SHA-256 over the raw fixture-file bytes.
+
+    Used as the canonical identity of a battery run; bench results
+    cite this digest so cross-run comparisons are unambiguous.
+    """
+    return hashlib.sha256(
+        Path(fixtures_path).read_bytes()
+    ).hexdigest()
+
+
+def iter_tasks(fixtures_path: Path) -> Iterable[dict]:
+    """Yield non-meta task dicts from a JSONL fixture file."""
+    with open(fixtures_path, "r", encoding="utf-8") as fh:
+        for line in fh:
+            line = line.strip()
+            if not line:
+                continue
+            obj = json.loads(line)
+            if "_meta" in obj:
+                continue
+            yield obj
+
+
+def fixture_meta(fixtures_path: Path) -> dict:
+    """Return the ``_meta`` dict if present at the top of the JSONL."""
+    with open(fixtures_path, "r", encoding="utf-8") as fh:
+        for line in fh:
+            line = line.strip()
+            if not line:
+                continue
+            obj = json.loads(line)
+            if "_meta" in obj:
+                return obj["_meta"]
+            return {}
+    return {}
diff --git a/bench/batteries/runner.py b/bench/batteries/runner.py
new file mode 100644
index 0000000..be2af7f
--- /dev/null
+++ b/bench/batteries/runner.py
@@ -0,0 +1,114 @@
+"""CLI entry: ``python -m bench.batteries.runner``.
+
+Runs one or more battery sub-batteries against their fixture files
+and emits a JSON result on stdout (or to ``--out`` if provided).
+
+Usage examples
+--------------
+
+::
+
+    # Run 5S Syntax + Semantics with the seed fixtures.
+    python -m bench.batteries.runner \\
+        --battery 5s --sub syntax --fixtures bench/fixtures/5s/syntax-v1.jsonl
+
+    python -m bench.batteries.runner \\
+        --battery 5s --sub semantics \\
+        --fixtures bench/fixtures/5s/semantics-v1.jsonl
+
+    # Run 5T Transfer.
+    python -m bench.batteries.runner \\
+        --battery 5t --sub transfer \\
+        --fixtures bench/fixtures/5t/transfer-v1.jsonl
+
+    # All Phase-1a fixtures, written to a results file.
+    python -m bench.batteries.runner --all --out bench/results/run.json
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import sys
+from dataclasses import asdict
+from pathlib import Path
+from typing import Optional
+
+from bench.batteries import b_5s, b_5t
+from bench.batteries.base import BatteryResult
+
+
+_BATTERIES = {
+    "5s": b_5s.SUB_BATTERIES,
+    "5t": b_5t.SUB_BATTERIES,
+}
+
+_DEFAULT_FIXTURES = {
+    ("5s", "syntax"): "bench/fixtures/5s/syntax-v1.jsonl",
+    ("5s", "semantics"): "bench/fixtures/5s/semantics-v1.jsonl",
+    ("5t", "transfer"): "bench/fixtures/5t/transfer-v1.jsonl",
+}
+
+
+def _run_one(battery: str, sub: str, fixtures: Path) -> BatteryResult:
+    if battery not in _BATTERIES:
+        raise SystemExit(f"unknown battery {battery!r}")
+    if sub not in _BATTERIES[battery]:
+        raise SystemExit(f"unknown sub-battery {sub!r} for {battery}")
+    return _BATTERIES[battery][sub](fixtures)
+
+
+def _emit(results: list[BatteryResult], out: Optional[str]) -> None:
+    payload = {
+        "schema_version": "bench-result-v1",
+        "results": [asdict(r) for r in results],
+    }
+    encoded = json.dumps(payload, indent=2, ensure_ascii=False, default=str)
+    if out:
+        Path(out).parent.mkdir(parents=True, exist_ok=True)
+        Path(out).write_text(encoded + "\n", encoding="utf-8")
+        print(f"wrote {out}")
+    else:
+        print(encoded)
+
+
+def main(argv: Optional[list[str]] = None) -> int:
+    p = argparse.ArgumentParser(description=__doc__)
+    p.add_argument("--battery", choices=sorted(_BATTERIES), default=None)
+    p.add_argument("--sub", default=None, help="sub-battery name")
+    p.add_argument("--fixtures", default=None, help="fixture JSONL path")
+    p.add_argument(
+        "--all",
+        dest="run_all",
+        action="store_true",
+        help="run all Phase-1a sub-batteries with default fixtures",
+    )
+    p.add_argument("--out", default=None, help="write JSON to this path")
+    args = p.parse_args(argv)
+
+    results: list[BatteryResult] = []
+    if args.run_all:
+        for (battery, sub), fixture_path in _DEFAULT_FIXTURES.items():
+            results.append(_run_one(battery, sub, Path(fixture_path)))
+    else:
+        if not args.battery or not args.sub:
+            p.error("--battery and --sub are required unless --all is given")
+        if args.fixtures:
+            fixtures = Path(args.fixtures)
+        else:
+            key = (args.battery, args.sub)
+            if key not in _DEFAULT_FIXTURES:
+                p.error(
+                    f"no default fixture for ({args.battery},{args.sub}); "
+                    "pass --fixtures explicitly"
+                )
+            fixtures = Path(_DEFAULT_FIXTURES[key])
+        results.append(_run_one(args.battery, args.sub, fixtures))
+
+    _emit(results, args.out)
+    failed = sum(r.fail_count for r in results)
+    return 1 if failed else 0
+
+
+if __name__ == "__main__":  # pragma: no cover
+    sys.exit(main())
diff --git a/bench/fixtures/5s/semantics-v1.jsonl b/bench/fixtures/5s/semantics-v1.jsonl
new file mode 100644
index 0000000..7c837b1
--- /dev/null
+++ b/bench/fixtures/5s/semantics-v1.jsonl
@@ -0,0 +1,9 @@
+{"_meta":{"battery":"5s","sub_battery":"semantics","version":"v1","task_count":8}}
+{"id":"5s-sem-001","kind":"equivalence","pi_star":"wikitext-base@v1","input_a":"hello world","input_b":"hello world","expected_equivalent":true}
+{"id":"5s-sem-002","kind":"equivalence","pi_star":"wikitext-base@v1","input_a":"hello   world","input_b":"hello world","expected_equivalent":true}
+{"id":"5s-sem-003","kind":"equivalence","pi_star":"wikitext-base@v1","input_a":"hello world","input_b":"goodbye world","expected_equivalent":false}
+{"id":"5s-sem-004","kind":"equivalence","pi_star":"wikitext-base@v1","input_a":"[[link|word]]","input_b":"word","expected_equivalent":true}
+{"id":"5s-sem-005","kind":"equivalence","pi_star":"wikitext-base@v1","input_a":"<ref>cite</ref>text","input_b":"text","expected_equivalent":true}
+{"id":"5s-sem-006","kind":"equivalence","pi_star":"claim-lattice@v1","input_a":"- A claim. [E1]","input_b":"- A claim. [E1]","expected_equivalent":true}
+{"id":"5s-sem-007","kind":"equivalence","pi_star":"claim-lattice@v1","input_a":"- A claim. [E1]","input_b":"- A different claim. [E1]","expected_equivalent":false}
+{"id":"5s-sem-008","kind":"equivalence","pi_star":"claim-lattice@v1","input_a":"- A claim. [E1]","input_b":"- A claim. [E2]","expected_equivalent":false}
diff --git a/bench/fixtures/5s/syntax-v1.jsonl b/bench/fixtures/5s/syntax-v1.jsonl
new file mode 100644
index 0000000..da87ebe
--- /dev/null
+++ b/bench/fixtures/5s/syntax-v1.jsonl
@@ -0,0 +1,11 @@
+{"_meta":{"battery":"5s","sub_battery":"syntax","version":"v1","task_count":10}}
+{"id":"5s-syn-001","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"Plain text.","expected":"pass"}
+{"id":"5s-syn-002","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"[[Wikilink]]","expected":"pass"}
+{"id":"5s-syn-003","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"''italic''","expected":"pass"}
+{"id":"5s-syn-004","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"'''bold'''","expected":"pass"}
+{"id":"5s-syn-005","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"== Header ==","expected":"pass"}
+{"id":"5s-syn-006","kind":"parse-pass","pi_star":"claim-lattice@v1","input":"- A claim. [E1]","expected":"pass"}
+{"id":"5s-syn-007","kind":"parse-pass","pi_star":"claim-lattice@v1","input":"- Another claim. [E2]","expected":"pass"}
+{"id":"5s-syn-008","kind":"parse-pass","pi_star":"claim-lattice@v1","input":"","expected":"pass"}
+{"id":"5s-syn-009","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"<ref>citation</ref> dropped","expected":"pass"}
+{"id":"5s-syn-010","kind":"parse-pass","pi_star":"wikitext-base@v1","input":"[[File:img.jpg|thumb]]","expected":"pass"}
diff --git a/bench/fixtures/5t/transfer-v1.jsonl b/bench/fixtures/5t/transfer-v1.jsonl
new file mode 100644
index 0000000..394d94f
--- /dev/null
+++ b/bench/fixtures/5t/transfer-v1.jsonl
@@ -0,0 +1,5 @@
+{"_meta":{"battery":"5t","sub_battery":"transfer","version":"v1","task_count":4,"note":"Phase 1 seed; full fixtures land in follow-up. Each task names a π* and asserts that canonicalize-then-canonicalize equivalence is preserved across paraphrase shapes drawn from a different surface form."}}
+{"id":"5t-xfer-001","kind":"paraphrase-invariance","pi_star":"wikitext-base@v1","input_a":"hello [[world]]","input_b":"hello [[world|world]]","expected_equivalent":true}
+{"id":"5t-xfer-002","kind":"paraphrase-invariance","pi_star":"wikitext-base@v1","input_a":"text\n\n\n\nmore","input_b":"text\n\nmore","expected_equivalent":true}
+{"id":"5t-xfer-003","kind":"paraphrase-invariance","pi_star":"claim-lattice@v1","input_a":"- A. [E1]\n- B. [E2]","input_b":"- A. [E1]\n- B. [E2]\n","expected_equivalent":true}
+{"id":"5t-xfer-004","kind":"paraphrase-invariance","pi_star":"claim-lattice@v1","input_a":"- A. [E1]","input_b":"- A. [E1, E2]","expected_equivalent":false}
diff --git a/docs/TICKETS.md b/docs/TICKETS.md
index cf49165..228ddca 100644
--- a/docs/TICKETS.md
+++ b/docs/TICKETS.md
@@ -58,7 +58,7 @@ Newest first. Update on every open/close.
 | ID       | Title                                          | Status                | Opened     | Directive |
 |----------|------------------------------------------------|-----------------------|------------|-----------|
 | #000022  | Adapter LossReport (PRD I9 analogue)           | open · awaiting go/no-go | 2026-05-07 | —         |
-| #000021  | 5S/5T/5R benchmark fixtures + harness          | open · awaiting go/no-go | 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 | —         |
 | #000018  | Adversarial soft-hash covert-channel analysis  | open · awaiting go/no-go | 2026-05-07 | —         |
diff --git a/docs/tickets/ticket-000021-bench-fixtures-5s-5t-5r.md b/docs/tickets/ticket-000021-bench-fixtures-5s-5t-5r.md
index 52e5576..e4512e1 100644
--- a/docs/tickets/ticket-000021-bench-fixtures-5s-5t-5r.md
+++ b/docs/tickets/ticket-000021-bench-fixtures-5s-5t-5r.md
@@ -1,6 +1,6 @@
 # Ticket #000021 — 5S/5T/5R benchmark fixtures + harness extension
 
-**Status:** open · awaiting go/no-go
+**Status:** in progress · Phase 1a landed 2026-05-07; Phase 1b + 2 + 3 open
 **Opened:** 2026-05-07
 **Scope:** Implement the SQD whitepaper's named bench batteries
 (5S Syntax/Semantics/Synthesis/Syllogism/Semiotics, 5T Transfer/
@@ -290,12 +290,44 @@ bench-5s5t: bench-5s bench-5t
 
 ## 7. Status
 
-**Open · awaiting go/no-go.** Mid-sized implementation surface
-(~600 lines code + 200-1000 fixtures). Recommended Phase 1 scope
-keeps it shippable in a single session for a focused operator;
-Phase 2/3 are future tickets.
+**In progress · Phase 1a landed 2026-05-07.** Skeleton + seed
+fixtures ship; full Phase 1 fixture authoring + Phase 2 (5R) +
+Phase 3 (external corpora) deferred to follow-up tickets.
 
-Closure criterion: `bench/fixtures/5s/`, `bench/fixtures/5t/`,
-`bench/batteries/{b_5s,b_5t,runner}.py` land; `make bench-5s5t`
-runs end-to-end against the existing shards and produces a JSON
-result file with all 10 battery slots populated.
+### Phase 1a (landed)
+
+- `bench/batteries/{base,b_5s,b_5t,runner}.py` — Battery protocol,
+  BatteryResult, fixture digest helpers, runner CLI.
+- `bench/fixtures/5s/syntax-v1.jsonl` — 10 seed tasks against
+  `wikitext-base@v1` and `claim-lattice@v1`. All pass.
+- `bench/fixtures/5s/semantics-v1.jsonl` — 8 seed tasks
+  (equivalence assertions). All pass.
+- `bench/fixtures/5t/transfer-v1.jsonl` — 4 seed tasks
+  (paraphrase-invariance). All pass.
+- Battery runners for **5S Syntax**, **5S Semantics**, and **5T
+  Transfer** are functional. Other 5S/5T sub-batteries are stubs
+  returning zero-task BatteryResults.
+- Makefile targets `bench-5s`, `bench-5t`, `bench-5s5t`.
+- Tests: `tests/test_bench_batteries.py` — 17 cases. Full suite:
+  1076 passed, 36 skipped.
+
+### Phase 1b (deferred)
+
+- Expand seed fixtures to 50-200 per sub-battery so signal floor
+  is meaningful (5pp tolerance over n≥3 runs).
+- Implement Synthesis, Syllogism, Semiotics under 5S; Triangulate,
+  Timing, Transitivity, Truth under 5T.
+
+### Phase 2 (deferred — depends on #000014 + #000017)
+
+- 5R battery (React/Rearrange/Restore/Replicate/Resonate) over a
+  workspace abstraction. Depends on SelfModel + memory_root being
+  the workspace surface.
+
+### Phase 3 (deferred)
+
+- External-corpus expansion. Cross-substrate transfer testing.
+
+Closure criterion (final): all three phases landed; full battery
+suite runs as `make bench-5s5t5r`. Phase 1a alone is not closure;
+ticket stays in-progress until Phase 1b lands.
diff --git a/tests/test_bench_batteries.py b/tests/test_bench_batteries.py
new file mode 100644
index 0000000..162a02b
--- /dev/null
+++ b/tests/test_bench_batteries.py
@@ -0,0 +1,156 @@
+"""5S/5T battery harness tests (ticket #000021 Phase 1a).
+
+Covers:
+- Fixture digest is stable across reads
+- 5S Syntax produces a non-empty BatteryResult on seed fixtures
+- 5S Semantics passes/fails as expected on seed fixtures
+- 5T Transfer passes/fails as expected on seed fixtures
+- Stub sub-batteries return zero-task results without error
+- Runner produces JSON-serializable output
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import asdict
+from pathlib import Path
+
+import pytest
+
+from bench.batteries import b_5s, b_5t
+from bench.batteries.base import (
+    BatteryResult,
+    fixture_digest,
+    fixture_meta,
+    iter_tasks,
+)
+
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+SYNTAX_FX = REPO_ROOT / "bench" / "fixtures" / "5s" / "syntax-v1.jsonl"
+SEM_FX = REPO_ROOT / "bench" / "fixtures" / "5s" / "semantics-v1.jsonl"
+XFER_FX = REPO_ROOT / "bench" / "fixtures" / "5t" / "transfer-v1.jsonl"
+
+
+def test_fixture_digest_stable():
+    a = fixture_digest(SYNTAX_FX)
+    b = fixture_digest(SYNTAX_FX)
+    assert a == b
+    assert len(a) == 64
+
+
+def test_fixture_meta_round_trip():
+    m = fixture_meta(SYNTAX_FX)
+    assert m["battery"] == "5s"
+    assert m["sub_battery"] == "syntax"
+    assert m["version"] == "v1"
+
+
+def test_iter_tasks_skips_meta():
+    tasks = list(iter_tasks(SYNTAX_FX))
+    assert all("_meta" not in t for t in tasks)
+    assert len(tasks) == 10
+
+
+def test_5s_syntax_runs():
+    res = b_5s.run_syntax(SYNTAX_FX)
+    assert isinstance(res, BatteryResult)
+    assert res.battery == "5s"
+    assert res.sub_battery == "syntax"
+    assert res.pass_count + res.fail_count == 10
+    # All seed fixtures should pass — they're chosen for active π*'s.
+    assert res.pass_count == 10
+    assert res.metrics["parse_pass_rate"] == 1.0
+    assert len(res.runtime_digest) == 64
+
+
+def test_5s_semantics_runs():
+    res = b_5s.run_semantics(SEM_FX)
+    assert res.battery == "5s"
+    assert res.sub_battery == "semantics"
+    # Seed fixtures are hand-curated to pass under current π*'s.
+    assert res.pass_count == res.pass_count + res.fail_count
+    assert res.metrics["equivalence_recovery_rate"] == 1.0
+
+
+def test_5t_transfer_runs():
+    res = b_5t.run_transfer(XFER_FX)
+    assert res.battery == "5t"
+    assert res.sub_battery == "transfer"
+    assert res.pass_count + res.fail_count >= 1
+
+
+@pytest.mark.parametrize(
+    "fn",
+    [
+        b_5s.run_synthesis,
+        b_5s.run_syllogism,
+        b_5s.run_semiotics,
+        b_5t.run_triangulate,
+        b_5t.run_timing,
+        b_5t.run_transitivity,
+        b_5t.run_truth,
+    ],
+)
+def test_stub_sub_batteries_return_zero(fn, tmp_path):
+    # Stub takes any path; doesn't read it.
+    res = fn(tmp_path / "missing.jsonl")
+    assert res.pass_count == 0
+    assert res.fail_count == 0
+
+
+def test_battery_result_is_json_serializable():
+    res = b_5s.run_syntax(SYNTAX_FX)
+    payload = json.dumps(asdict(res), default=str)
+    assert "syntax" in payload
+
+
+def test_runner_main_smoke(tmp_path, capsys):
+    """Runner produces JSON on stdout when --out is omitted."""
+    from bench.batteries.runner import main
+
+    rc = main(
+        [
+            "--battery",
+            "5s",
+            "--sub",
+            "syntax",
+            "--fixtures",
+            str(SYNTAX_FX),
+        ]
+    )
+    out = capsys.readouterr().out
+    payload = json.loads(out)
+    assert payload["schema_version"] == "bench-result-v1"
+    assert payload["results"][0]["battery"] == "5s"
+    assert rc == 0
+
+
+def test_runner_writes_to_file(tmp_path):
+    from bench.batteries.runner import main
+
+    out_path = tmp_path / "result.json"
+    rc = main(
+        [
+            "--battery",
+            "5s",
+            "--sub",
+            "semantics",
+            "--fixtures",
+            str(SEM_FX),
+            "--out",
+            str(out_path),
+        ]
+    )
+    assert rc == 0
+    payload = json.loads(out_path.read_text())
+    assert payload["results"][0]["sub_battery"] == "semantics"
+
+
+def test_runner_all_runs_phase_1a():
+    """--all runs all three default fixtures and exits 0 when all pass."""
+    from bench.batteries.runner import main
+
+    rc = main(["--all"])
+    # All seed fixtures are constructed to pass; rc=0 expected.
+    assert rc == 0