docs(operations): record CR-DD-016 Track B classifier-fallback investigation

[coreytshaffer]

Summary

Read-only investigation record for Track B of CR-DD-016's Sequencing section, which required that track stay read-only "until its own findings warrant a separately scoped CR." This is that read-only output. One new file, 301 lines, documentation only.

No CR identifier is minted, no implementation authority is requested or granted, and no triage_core/ source, schema, test, or fixture is changed by this PR.

Track B was scoped to settle three questions. All three are now answered:

1. Is "refactor" genuinely the universal terminal fallback? Yes. classify_deterministic's terminal no-match return (classifier.py:78) is reached by every path through classify (classifier.py:58) — no backend, construction failure, exception, timeout, empty response, or non-member response. Confirmed empirically: the empty string classifies as refactor.

2. What downstream routing depends on it? This sharpens CR-DD-016's characterization. That CR called the fallback "semantically wrong"; the record establishes it is wrong in the permissive direction — refactor maps to sensitivity="low", routes to local_heavy, and yields human_review_required=False. An unclassifiable prompt fails toward autonomous execution rather than toward review. This is a property of the composition of classifier.py and client.py's maps; neither file states it.

3. Did any trial traverse it? The Aug-8 trial motivating CR-DD-016 provably did not — confirming that CR's Corrective Amendment by probe rather than by inference. But the general question is unanswerable from recorded evidence by construction: bugfix and refactor both collapse onto task_class=code_repair before anything is written, so the two code_repair trials in 2026-08-01-corrected are permanently ambiguous.

Method, and its limits

Static inspection at fa66c64; probes that call the real _build_resilience_route_input and choose_resilience_route rather than re-implementing their logic; a read-only census of every route_audit/route_decision pair in the repository's ledgers. No tc run invoked, no ledger written, no synthetic execution created.

Stated plainly in the document rather than buried: measuring the timeout required five live local Ollama calls. They wrote nothing and touched no ledger, route, capability, privacy, or authority surface, but two findings depend on them.

Two deliberate non-assertions:

• The 0/5 race result is scoped to one host, one cold model, one moment. The record explicitly does not claim the model path never wins anywhere — which is what makes the divergence a race rather than a constant.
• The ~3015 ms cost of the nominal 1.5 s guard is measured but not explained. A refuted hypothesis (that resolve_model burns a second budget — it measures 0 ms, short-circuiting on an explicit model) is kept in the record, and the cause inside requests/urllib3 is left unisolated rather than guessed at.

Reconciliation against current main

main advanced three times while this was drafted. The record carries a reconciliation section rather than reading as current when part of it no longer is:

merge	PR	touched triage_core/?	affects the record?
c798e0e	#179 CR-DD-012B	yes	Yes — overlaps Finding 3
da96b66	#180 CR-DD-016 closeout	no	no
96eb3d3	#166 CR-132	no	no

PR #179 landed CLASSIFICATION_REASON_CODES (governed_decision.py:65-72) distinguishing deterministic_classifier_default from deterministic_classifier_match — exactly the provenance Finding 3 reports as absent, so Finding 3 is recorded as partially superseded for the governed-decision path. It is not fully resolved: the ordinary tc run path still classifies without provenance (client.py:215) and still collapses bugfix/refactor (client.py:774-821). Whether the governed reason reaches persisted route evidence is left explicitly untraced, not asserted.

Findings 1, 2 and 4–7 stand: git diff c798e0e 96eb3d3 -- triage_core/ tests/ schemas/ is empty, and classifier.py, resilience_router.py, backends.py are byte-identical to fa66c64.

Test plan

• Cumulative diff is exactly one new file under docs/operations/. No non-docs/ path touched; git status clean throughout.
• All 25 file:line citations in the findings verified to resolve to the text attributed to them at fa66c64.
• All reconciliation citations re-verified against 96eb3d3.
• Citation drift re-checked using the two stale anchors as negative controls — run_plan.py:59 and route_events.py:217 still resolve to the wrong content at 96eb3d3, confirming the drift is a real property of the record rather than an artifact of the checking method.
• Router envelope derived by probing the real router across all 8 categories at the Aug-8 trial's recorded capability state, not by mirroring candidate logic.
• Probe module provenance asserted at runtime (triage_core.__file__ pinned to this worktree) so results are not silently taken from the main checkout.
• Verified the file is absent on main — clean add, no conflict.

No test-suite run: this PR adds a documentation record and changes no code.

What this does not grant

Merge authority for this PR. Any implementation change to the classifier or its maps. Any reopening of CR-DD-016, its Corrective Amendment, or its closeout. Any resolution of Track C, which remains untouched and separately scoped.

The record recommends two future CRs — fallback semantics/execution-path provenance, and classifier provenance/divergence — deliberately not combined, per the sequencing rule CR-DD-017 restates. Candidate 1 is explicitly narrowed so it does not re-scope what #179 already merged. Neither is proposed here.

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