diff --git a/docs/evals/2026-09-08-slice23-fast-path-metadata-reconciliation.md b/docs/evals/2026-09-08-slice23-fast-path-metadata-reconciliation.md
new file mode 100644
index 0000000..59508e4
--- /dev/null
+++ b/docs/evals/2026-09-08-slice23-fast-path-metadata-reconciliation.md
@@ -0,0 +1,190 @@
+# Rebuilding corpus fast-path metadata from the real router moves the slice-22 1652-row five-way numbers by ≤2pp (heads 0.772→0.751 acc, e5-linear 0.722/0.712→0.720/0.731 macro-F1) and every aggregate slice-22 conclusion survives, so the learned non-action router investigation is closed as run; the residual pool is 1509 non-action + 720 action OOD rows, and the deterministic hash-classifier floor collapses to acc 0.066 because its earlier 0.171 was almost entirely the 185 rows the stale mirror had mislabelled as residual while the real grammars already resolve them
+
+Date: 2026-09-08 · Task: slice 23 (fast-path metadata reconciliation; postscript to the accepted slice 22, task/725) · Box: workpc, Arch, RX 7900 GRE, 32 GB · Build: `internal/router/semantic/fastpath.go` + `cmd/semantic-router-experiment/slice23/` (Go 1.25.12) + `slice23_emit.py`/`slice23_main.py` in the frozen venv `/tmp/mvn-exp-venv` (sklearn 1.9.0); ONNX via `MAVEN_ONNX_LIB` pointing at the venv's `libonnxruntime.so.1.29.0`.
+
+Replaces the corrected-population numbers in [slice 22](2026-09-08-slice22-residual-nonaction-router.md). The slice-22 file keeps its role for the run itself; its 1652-row pool is no longer the current measurement population.
+
+## 0. What changed and what did not
+
+The corpus's `fast_path_resolved` flag was stamped by a hand-written regex mirror
+(`classifyFastPath` in `cmd/corpus-factory/main.go`) that drifted from the
+stage-0 grammars. Slice 22 noticed 185 residual rows resolving at runtime. This
+slice makes the flag a derivation from the real router and re-measures.
+
+```text
+corpus 3025 rows, dev pool 2490, frozen holdout 535            unchanged
+dataset_hash b27fd48f478ca477cab1e59773bb353a                  unchanged (texts)
+fast_path_resolved      82 → 271   (dev 72 → 261, frozen 10, preserved)
+residual                2943 → 2754 (dev 2418 → 2229, frozen 525, preserved)
+residual non-action pool 1652 → 1509
+  knowledge 715→558 / memory_write 553→541 / system 184→220 / conversation 93→91 / uncertain 107→99
+action OOD probes        766 → 720
+residual dev pool folds {0:317,1:140,2:410,3:408,4:377} → {0:247,1:111,2:373,3:386,4:392}
+```
+
+The rebuild changed **exactly the derived fields on exactly the 277 dev rows**
+that disagree with the router: 0 rows differ in text, route, source, source_id,
+split_group, or the non-`router_residual` tags. The 22 stale frozen rows (see §1)
+are preserved verbatim per the merge rule — reported, never silently rewritten.
+
+## 1. The drift, decomposed (299 disagreements across 3025 corpus rows)
+
+`cmd/semantic-router-experiment/slice23` runs `DeriveFastPath` (the production
+`TryFastPath` over `StageZeroGrammars` with the experiment act allowlist) on
+every row and attributes the winner. Output: `/tmp/mvn-s23/drift.json`.
+
+```text
+mirror_missed (stored residual, runtime resolves)      249
+  dev 233  = 185 non-action + 48 action
+    dev non-action by grammar: calendar-query 66, definition-query 30,
+      narrative-query 26, task-capture 12, agenda-query 9, task-list-query 9,
+      plan-day-query 8, ambiguous-fragment 7, time-query 6, rest-of-day 5,
+      event-time 4, possession-statement 2, reminder-wakeword 1
+  frozen 16 (possession 6, implicit-elapsed 3, wakeword-act 2, + 5 singles)
+claimed_fast_now_miss (stored fast, runtime declines)   50
+  dev 44 (system 42, action 2) + frozen 6 (memory_write "note: " rows)
+  every one has ≥1 stage-0 grammar matching its shape and declining the build;
+  none is a "no grammar matches" row
+```
+
+The **185 dev non-action `mirror_missed` rows are byte-identical in count and
+route split** to the slice-22 harness's `grammar_hits_in_pool: 185`
+(knowledge 157, memory_write 12, system 6, conversation 2, uncertain 8) — a
+strong cross-check that `DeriveFastPath` equals what the slice-22 harness
+measured through `Route()`.
+
+Root cause, two mechanisms:
+
+1. **Grammar coverage grew after the corpus froze.** `calendar-query` (67),
+   `definition-query` (31), `narrative-query` (27), `task-status` (24),
+   `agenda-query` (9), `possession-statement` (8), `plan-day-query` (8),
+   `event-time-query` (4) and the rest are current stage-0 rules with no
+   counterpart in the mirror. The mirror ever only knew a fixed verb list.
+2. **The mirror's verb lists over-stamped.** The 50 `claimed_fast_now_miss`
+   rows ("покажи uptime", "note: кран на кухне капает", "what's the date
+   сегодня") matched `toolAliasRe`/`captureVerbRe`/`timeQueryRe`, but no real
+   grammar accepts them: rules like `task-list-query`/`list-capture` use a
+   catch-all `(?s)^\s*(.+)$` pattern with the real gate in `Build`, which
+   declines. The mirror had no concept of a build gate.
+
+The frozen 22 (16 + 6) are the same two mechanisms on holdout families,
+including three `ru_routing_v1` rows ("что у меня стоит в календаре на
+послезавтра", "расскажи про битву при Ватерлоо", "кто такой Линус Торвальдс?")
+now resolved by calendar/narrative/definition grammars.
+
+## 2. The authoritative derivation
+
+`internal/router/semantic/fastpath.go` (non-test) owns:
+
+- `ExperimentActVerbs()` — the 18 verbs formerly duplicated in
+  `helpers_test.go`, `legacy_build.go` and `heads_main.go`; now one non-test
+  list, so propagation can never drift from measurement.
+- `DeriveFastPath(text) FastPathOutcome{Matched, Grammar}` — builds the exact
+  router the legacy baseline measures (`router.StageZeroGrammars` + the
+  experiment act matcher + `StubDateTimeParser`/`DefaultFactParser`) and runs
+  `TryFastPath(NormalizedInput{Text, MatchText: NormalizeMatchText(Text)})`.
+  Grammar attribution replays the ordered first-accept walk the router performs,
+  including wake-stripped alternates and build-declined fall-through.
+
+Consumers:
+
+- `cmd/corpus-factory` stamps `fast_path_resolved`/`router_residual` from
+  `DeriveFastPath`; the regex mirror is deleted.
+- `cmd/merge-corpus` validates every v2 row against the derivation and **fails
+  on a stale value**; frozen holdout drift is reported only.
+- `internal/router/semantic/fastpath_invariant_test.go` asserts every dev row
+  satisfies `fast_path_resolved == DeriveFastPath(text).Matched`; frozen rows
+  are exempt by the merge rule.
+
+## 3. Rebuild proofs
+
+```text
+factory v2:  3008 rows, text-set identical old↔new
+             diff = exactly the fast-path fields on 296 rows; 0 other diffs
+merge:       v2 dev rows 2490 all validated against the router (0 stale)
+             frozen 535 preserved; 22 drift rows reported, none rewritten
+v1 embedded: 3025 rows, text-set identical; dataset_hash unchanged
+             diff = fast-path fields on the 277 dev rows; 0 other diffs
+embeddings:  regenerated (fast_path_count 82 → 271, residual_count 2943 → 2754)
+             all 3025 vectors differ by ≤ ~0.02 max-abs from the slice-22 file
+             (onnxruntime build noise); on the same 1509 pool the e5-linear
+             score moves only −0.0014 acc / −0.0002 macro-F1 (C=10), i.e. the
+             population effect, not the embedding noise, drives every delta
+```
+
+## 4. Baseline deltas on the corrected population
+
+| measure | slice 22 (n=1652) | slice 23 (n=1509) |
+| --- | --- | --- |
+| legacy hash floor | 0.1707 / 0.1202 (illegal 3) | **0.0663 / 0.0265 (illegal 2)** |
+| deployed cascade (heads) | 0.7724 / 0.7150 (illegal 143) | 0.7515 / 0.7065 (illegal 142) |
+| e5-linear C=10 | 0.7222 / 0.7117 | 0.7203 / 0.7310 |
+| centroid (cosine) | 0.6731 / 0.6494 | 0.6753 / 0.6494 |
+| sparse word+char (both) | 0.6247 / 0.4463 (vocab 6951) | 0.5991 / 0.4588 |
+| majority | 0.4328 / 0.1208 | 0.3698 / 0.1080 |
+| leave-one-family-out | 0.6824 / 0.1499, 53 fm | 0.6863 / 0.1519, 53 fm |
+| fact holdout | 0.0180 (n 389) | 0.0077 (n 389) |
+| world holdout | 0.7622 (n 143) | 0.6552 (n 87) |
+| recall holdout | 0.7632 (n 114) | 0.5667 (n 90) |
+| calendar holdout | 0.6304 (n 92) | 0.5185 (n 27) |
+| K/MW water pairs | 0.863 (480), +0.298 | 0.850 (480), +0.275 |
+| K/MW homelab pairs | 0.106 (180), −0.228 | 0.072 (180), −0.247 |
+| K/MW task pairs | 0.735 (720), +0.122 | 0.403 (216), −0.095 |
+| uncertain OOF P/R/F1 | 0.758 / 0.701 / 0.728 | 0.734 / 0.697 / 0.715 |
+| action OOD swallowed | knowledge 370, mw 347 of 766 (conf>0.9: 0.060) | knowledge 364, mw 312 of 720 (conf>0.9: 0.056) |
+| grammar hits in pool | 185 / 1467 pure | **0 / 1509 pure** |
+
+The hash floor's collapse is explained structurally: the 185 removed rows were
+nearly all the hash classifier's correct knowledge hits (correct predictions
+282 → 98, a one-to-one loss with the drift), so the deterministic floor "resolves"
+the same rows the real grammars already own.
+
+## 5. The decisions requested
+
+1. **Drift decomposition** — §1; 299 = 249 + 50; the slice-22 185 reproduces exactly.
+2. **Root cause** — §1; coverage growth + build-gate over-stamp, neither visible to a regex mirror.
+3. **Authoritative derivation** — §2; `DeriveFastPath` on the standard experiment router; duplicated act list removed.
+4. **Corpus-builder change** — §2-§3; factory stamps from the router, merge validates (fail on stale) + reports frozen drift, invariant test enforces it.
+5. **Corrected counts** — §0; fast 82→271, residual 2943→2754, pool 1652→1509 non-action + 720 OOD; dataset hash unchanged proves only the derived field moved.
+6. **Baseline deltas** — §4; all ≤2pp on the head scores; hash floor collapses because its output was the drifted rows.
+
+## 6. Conclusion survival and the gate
+
+Every aggregate slice-22 conclusion is unchanged on the corrected population:
+
+- **e5-linear ≈ deployed cascade.** e5 0.7203 vs heads 0.7515 acc (slice 22:
+  0.7222 vs 0.7724); macro-F1 e5 0.7310 now *exceeds* heads 0.7065. The ≈3pp
+  gap stands; a head on frozen e5 embeddings adds nothing a linear probe lacks.
+- **Cross-family transfer is structurally absent.** LOFO macro-F1 0.1519;
+  fact holdout 0.0077; system/conversation/uncertain holdouts 0.0000.
+- **K/MW is a deterministic semantic defect.** Homelab pairs still order
+  backwards (0.072, margin −0.247); task pairs now order backwards too
+  (0.403, margin −0.095, pairs 720→216 as the calendar/task queries leave the
+  pool). Water stays right (0.850). No learned head fixes this at the margin.
+- **The deterministic floor is not a baseline.** acc 0.0663 ≈ predicting
+  uncertain for everything.
+- **Action OOD is still swallowed.** 676 of 720 (93.9%) land in
+  knowledge/memory_write at argmax; conf>0.9 5.6%.
+
+Decision gate from the brief: conclusions **materially the same**. The learned
+non-action-router investigation is **closed**; no new representation or head is
+justified. Next slice: the note-vs-recall disambiguator (the one genuine residual
+deterministic defect the K/MW numbers keep surfacing).
+
+## Artifacts
+
+Re-run (corrected population):
+
+```sh
+go run ./cmd/semantic-router-experiment/slice23/ -out /tmp/mvn-s23/drift.json
+go build -o /tmp/mvn-s23/s23 ./cmd/semantic-router-experiment/slice22/
+MAVEN_ONNX_LIB=…/libonnxruntime.so.1.29.0 /tmp/mvn-s23/s23 -mode legacy -pool /tmp/mvn-s23/pool.json -out /tmp/mvn-s23/legacy.json
+MAVEN_ONNX_LIB=… /tmp/mvn-s23/s23 -mode heads -pool /tmp/mvn-s23/pool.json -out /tmp/mvn-s23/legacy_heads.json
+python3 slice23_emit.py            # → /tmp/mvn-s23/{pool,ood,stats}.json (1509/720)
+MAVEN_ONNX_LIB=… python3 slice23_main.py   # → /tmp/mvn-s23/results.json
+```
+
+Corpus rebuild (proofs in §3): `corpus-factory -out /tmp/corpus_v2.json`, then
+`merge-corpus -v1 corpus_v1.json -v2 /tmp/corpus_v2.json -out corpus_v1.json`
+(identity of the change verified against `/tmp/mvn-s23/corpus_v1.old.json`).
+Embedding regeneration (noise isolation against `/tmp/mvn-s23/embeddings.old.json`).
\ No newline at end of file
diff --git a/docs/evals/CLAUDE.md b/docs/evals/CLAUDE.md
index 5f96dc8..e1b7a34 100644
--- a/docs/evals/CLAUDE.md
+++ b/docs/evals/CLAUDE.md
@@ -54,7 +54,8 @@ A pair in `docs/routing.md` went stale unnoticed. Its source predated the
 | [From-scratch tiny sequence pragmatics specialist (slice 19)](2026-09-08-tiny-sequence-pragmatics-specialist.md) | live |
 | [Pretrained rubert-tiny pragmatics baseline (slice 20)](2026-09-07-pretrained-rubert-tiny-pragmatics-baseline.md) | live |
 | [Deterministic execution-frame guard (slice 21)](2026-09-07-execution-frame-guard.md) | live |
-| [Five-way residual non-action router: linear e5 vs the deployed cascade (slice 22)](2026-09-08-slice22-residual-nonaction-router.md) | live |
+| [Five-way residual non-action router: linear e5 vs the deployed cascade (slice 22)](2026-09-08-slice22-residual-nonaction-router.md) | superseded by 2026-09-08-slice23 |
+| [Fast-path metadata rebuilt from the real router: the slice-22 numbers, corrected (slice 23)](2026-09-08-slice23-fast-path-metadata-reconciliation.md) | live |
 
 `docs/routing.md` holds the arm table these feed. Cite from there, not from here.