build(qual): establish protected mutation dependency authority

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/CHUNK_MAP.md

@@ -21,13 +21,14 @@ remain stopped historical experiments. Do not resume them.
 | Chunk | Purpose | Risk | State |
 |---|---|---:|---|
 | `WS-QUAL-001-PLAN3` | Replace percentage-only closure with behavior/mutation assurance | L1 | Merged PR #272; late review corrected by PLAN3R1 |
-| `WS-QUAL-001-PLAN3R1` | Resolve five valid late CodeRabbit findings from PR #272 | L1 | Corrective planning chunk in progress |
-| `WS-QUAL-001-04M` | Pilot pinned changed-scope mutation evidence without a score gate | L1 | Proposed after PLAN3R1 merge and explicit instruction |
+| `WS-QUAL-001-PLAN3R1` | Resolve five valid late CodeRabbit findings from PR #272 | L1 | Merged PR #278 |
+| `WS-QUAL-001-04P` | Establish protected hash-verified mutation dependency authority | L1 | In progress by explicit instruction |
+| `WS-QUAL-001-04M` | Pilot pinned changed-scope mutation evidence without a score gate | L1 | Proposed after 04P merge and explicit instruction |
 | `WS-QUAL-001-05M` | Add calibrated blocking behavior-mutation policy | L1 | Proposed only after accepted 04M hosted evidence and explicit instruction |
 
 ## Dependency rule
 
-`PLAN3 -> PLAN3R1 -> 04M -> human calibration checkpoint -> 05M`.
+`PLAN3 -> PLAN3R1 -> 04P -> 04M -> human calibration checkpoint -> 05M`.
 
 Each chunk maps to one PR. `04M` may prove that the candidate engine or target
 strategy is unsuitable and stop without `05M`. Planning does not pre-authorize

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/STATUS.md

@@ -12,9 +12,13 @@ new or materially changed subsystem checks remain blocking at 90 percent.
 
 ## Current gate
 
-`WS-QUAL-001-PLAN3` merged through PR #272. `WS-QUAL-001-PLAN3R1` is a
-planning-only correction for five valid CodeRabbit findings that arrived before
-the merge but were not addressed. It must merge before `04M` starts.
+`WS-QUAL-001-PLAN3` merged through PR #272. Its planning-only correction
+`WS-QUAL-001-PLAN3R1` merged through PR #278 after resolving all late CodeRabbit
+findings.
+
+`WS-QUAL-001-04P` is now the active bounded prerequisite. It establishes the
+protected, exactly pinned, hash-verified mutation dependency authority. It does
+not execute mutation testing or start `04M`.
 
 The corrected proposal remains two-stage:
 
@@ -24,11 +28,10 @@ The corrected proposal remains two-stage:
 3. `05M` — separately approved blocking survivor policy for eligible changed
    logic and explicit test-only behavior claims.
 
-No mutation dependency, workflow, policy script, or blocking check has been
+No mutation workflow, policy script, execution, or blocking check has been
 implemented.
 
 ## Stop condition
 
-Stop after the PLAN3R1 correction review and PR. Do not start 04M automatically.
-Do not start 05M without accepted exact hosted pilot evidence and a new human
-instruction.
+Stop after the 04P review and PR. Do not start 04M automatically. Do not start
+05M without accepted exact hosted pilot evidence and a new human instruction.

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/README.md

@@ -4,6 +4,7 @@ Only these PLAN3 records describe possible current work:
 
 - `WS-QUAL-001-PLAN3-behavior-mutation-assurance.md`
 - `WS-QUAL-001-04M-changed-scope-mutation-pilot.md`
+- `WS-QUAL-001-04P-protected-mutation-dependency-authority.md`
 - `WS-QUAL-001-PLAN3R1-late-external-review-correction.md`
 - `WS-QUAL-001-05M-blocking-behavior-mutation-gate.md`
 

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/WS-QUAL-001-04M-changed-scope-mutation-pilot.md

@@ -67,12 +67,16 @@ checkout credentials, secrets in mutation execution, or unpinned Actions
 
 - [ ] One engine and transitive closure are exactly pinned and hash locked as
       development/CI-only dependencies. Pull-request checks obtain the
-      approved package, version, and hash authority from the protected base
-      revision (or an equivalently protected allowlist or prebuilt runtime),
-      never from a requirements manifest editable by the pull request.
+      approved package, version, and hash authority only from the protected
+      base-revision copy of `scripts/mutation-requirements.txt`, never from a
+      requirements manifest editable by the pull request. An alternate
+      allowlist or prebuilt runtime is not valid authority for 04M.
 - [ ] That protected dependency authority exists before the 04M branch starts;
       04M cannot introduce or modify it. If no approved authority exists, 04M
       stops for a separate bounded prerequisite rather than installing a tool.
+- [ ] The only dependency authority is the protected base-revision copy of
+      `scripts/mutation-requirements.txt`, introduced by 04P; 04M verifies and
+      installs that exact copy with `pip --require-hashes`.
 - [ ] `backend/pyproject.toml` contains configuration only; the mutation engine
       is absent from production dependencies and ordinary dev extras.
       `backend/uv.lock` remains unchanged and is not a second install path.

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/WS-QUAL-001-04P-protected-mutation-dependency-authority.md

@@ -0,0 +1,91 @@
+# Chunk Contract: WS-QUAL-001-04P — Protected Mutation Dependency Authority
+
+## Goal
+
+Place one reviewed, exactly pinned, hash-verified mutation-tool dependency
+authority on protected `main` before the separately started 04M pilot.
+
+## Why this chunk exists
+
+04M must not install a mutation toolchain selected by its own pull request.
+Protected `main` therefore needs to own the approved engine and complete
+transitive dependency manifest first.
+
+## Risk class
+
+L1 — development/CI supply-chain prerequisite.
+
+## Allowed files
+
+```text
+scripts/mutation-requirements.in
+scripts/mutation-requirements.txt
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/CHUNK_MAP.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/STATUS.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/README.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/WS-QUAL-001-04M-changed-scope-mutation-pilot.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/chunks/WS-QUAL-001-04P-protected-mutation-dependency-authority.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-internal-review-evidence.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-external-review-response.md
+.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-pr-trust-bundle.md
+```
+
+## Not allowed
+
+```text
+workflow or mutation execution
+backend application, test, pyproject, or uv.lock changes
+production dependency changes
+coverage-threshold or existing CI changes
+automatic start of 04M or 05M
+```
+
+## Acceptance criteria
+
+- [ ] `mutmut==3.7.0` is the sole mutation engine.
+- [ ] The complete transitive closure is exactly pinned and every requirement
+      carries one or more SHA-256 hashes.
+- [ ] The mutation runner uses the backend-aligned `pytest==8.4.2` and
+      `coverage==7.15.2` versions, and every other overlapping package matches
+      `backend/uv.lock`.
+- [ ] A clean Python 3.12 `pip --require-hashes` dry run accepts the manifest,
+      and Python 3.11 resolves a complete compatible hashed wheel set.
+- [ ] The manifest contains no project production dependency or index override.
+- [ ] 04M may read only the protected base-revision manifest and cannot modify
+      either authority file.
+- [ ] Apart from `scripts/mutation-requirements.in` and its compiled manifest,
+      no workflow, Backend runtime, test, production dependency, lockfile, or
+      coverage gate changes.
+
+## Verification commands
+
+```bash
+mutation_tmp=$(mktemp -d)
+python3.12 -m venv "$mutation_tmp/venv"
+"$mutation_tmp/venv/bin/python" --version
+"$mutation_tmp/venv/bin/python" -m pip install --dry-run --require-hashes -r scripts/mutation-requirements.txt
+python3 scripts/check_markdown_links.py
+python3 scripts/check_stale_workstream_wording.py
+python3 scripts/check_stale_authorization_docs.py
+python3 scripts/check_stale_artifact_contracts.py
+PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python3 -m pytest -q scripts/test_lightweight_agent_gates.py
+git diff --check
+```
+
+## Required reviewers
+
+- security/auth
+- CI integrity
+- reuse/dedup
+- docs
+
+## Human review focus
+
+Confirm the manifest is development/CI-only, exactly pinned and hashed, aligned
+with the backend test toolchain, and immutable to 04M PR-head code.
+
+## Stop conditions
+
+Stop if the engine cannot coexist with the backend's Python 3.11/3.12 contract,
+requires a production dependency change, or cannot be installed with hash
+checking enabled.

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-external-review-response.md

@@ -0,0 +1,36 @@
+# WS-QUAL-001-04P External Review Response
+
+## Comments addressed
+
+- 04M now names only the protected base-revision
+  `scripts/mutation-requirements.txt` as dependency authority and explicitly
+  rejects an alternate allowlist or prebuilt runtime for this pilot.
+- The 04P acceptance criterion now permits its two authority files while
+  preserving the prohibition on production dependency, lockfile, workflow,
+  Backend, test, and coverage-gate changes.
+- The verification command now creates a disposable Python 3.12 virtual
+  environment, records its interpreter version, and runs the hash-checked dry
+  run through that environment's Python executable.
+
+## Comments deferred
+
+None.
+
+## Commands rerun
+
+- Disposable Python 3.12 `pip --dry-run --require-hashes`: passed for all 20
+  dependencies.
+- `python3 scripts/check_markdown_links.py`: passed.
+- `PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python3 -m pytest -q scripts/test_lightweight_agent_gates.py`:
+  10 passed.
+- `git diff --check`: passed.
+
+## CI status at repair time
+
+Agent Gates and CodeRabbit passed on the prior remote head. The five Backend
+lanes were pending, not failed. Rebasing onto current `main` intentionally
+restarts exact-head checks.
+
+## Remaining risk
+
+None for 04P dependency custody. Mutation behavior and runtime remain 04M work.

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-internal-review-evidence.md

@@ -0,0 +1,38 @@
+# WS-QUAL-001-04P Internal Review Evidence
+
+## Reviewed scope
+
+- Reconciled base: `c7270d1969830f436a8f119c0dc771785ca0c62a`
+- Reviewed implementation head: `275f0d104f95b09329cc96713d94810589193318`
+- Seven changed paths: two dependency-authority files and five QUAL planning
+  records.
+- No workflow, Backend runtime, test, pyproject, lockfile, coverage command, or
+  threshold change.
+
+## Reviewer results
+
+| Track | Result | Disposition |
+|---|---|---|
+| Security/auth | PASS | All 20 requirements are exact and SHA-256 hashed; no index, path, VCS, editable, trusted-host, or nested-requirement override exists. |
+| CI integrity | PASS | Manifest is development/CI-only; no existing CI or coverage gate changed. |
+| Reuse/dedup | PASS after fix | Aligned `packaging==26.2`; all nine packages shared with `backend/uv.lock` now match exactly. |
+| Docs | PASS | Contract, status, chunk map, regeneration command, and 04M handoff are consistent. |
+
+## Deterministic evidence
+
+- Python 3.12 clean `pip --dry-run --require-hashes`: passed for all 20
+  requirements.
+- Python 3.11 cross-platform hashed wheel resolution: passed for all 20
+  requirements.
+- Static manifest validation: 20 exact pins, every entry hashed, no index
+  override.
+- Markdown links, stale wording, stale authorization docs, stale artifact
+  contracts, diff integrity, and 10 lightweight Agent Gates: passed.
+- CodeRabbit follow-up: unified 04M on the base-revision manifest, corrected the
+  production-dependency scope statement, and proved a disposable Python 3.12
+  verification command.
+
+## Remaining risk
+
+Tool behavior, mutant quality, and hosted runtime remain intentionally unproved
+until separately started 04M. This chunk establishes dependency custody only.

.agent-loop/initiatives/WS-QUAL-001-backend-coverage-floor/reviews/WS-QUAL-001-04P-pr-trust-bundle.md

@@ -0,0 +1,107 @@
+# WS-QUAL-001-04P PR Trust Bundle
+
+## Chunk
+
+`WS-QUAL-001-04P` — Protected Mutation Dependency Authority.
+
+## Goal
+
+Establish a protected-main mutation-tool dependency authority before 04M so
+untrusted PR-head code cannot select its own toolchain.
+
+## Human-approved intent
+
+The user explicitly instructed the orchestrator to start this prerequisite.
+04M is not started by this PR.
+
+## What changed
+
+- Added a small source authority pinning `mutmut==3.7.0` and backend-aligned
+  pytest, Coverage, and Packaging versions.
+- Added the generated complete 20-package SHA-256 manifest.
+- Updated QUAL sequencing and the 04M contract to consume only the protected
+  base-revision manifest.
+
+## Why it changed
+
+Hashes verify downloaded bytes but do not make PR-selected packages trusted.
+The approved package/version/hash set must exist on protected `main` before the
+04M branch can use it.
+
+## Design chosen
+
+`scripts/mutation-requirements.in` is the human-reviewed source list;
+`scripts/mutation-requirements.txt` is the complete generated install authority.
+04M reads the protected base copy and installs with `pip --require-hashes`; it
+cannot modify either file.
+
+## Alternatives rejected
+
+- Let 04M create its own hashed lock: PR code would still choose the packages.
+- Add mutmut to production or ordinary backend dev dependencies: unnecessary
+  coupling and lock churn.
+- Prebuilt image now: more infrastructure than this bounded prerequisite needs.
+
+## Scope control
+
+Only the two authority files and QUAL planning/review records change. No
+workflow, Backend runtime, test, lockfile, or coverage policy changes.
+
+## Product behavior
+
+None.
+
+## Acceptance criteria proof
+
+- Engine: `mutmut==3.7.0`.
+- Complete closure: 20 exact pins, all SHA-256 hashed.
+- Backend-aligned overlap: all nine shared packages match `backend/uv.lock`.
+- Python 3.12 hash-checked dry run: passed.
+- Python 3.11 compatible hashed wheel resolution: 20/20 passed.
+
+## Tests/checks run
+
+- Clean Python 3.12 `pip --dry-run --require-hashes`.
+- Python 3.11 cross-platform `pip download --require-hashes`.
+- Static exact-pin/hash/index validation.
+- Markdown links and all stale-document scans.
+- 10 lightweight Agent Gates.
+- `git diff --check`.
+
+## Test delta
+
+No test changed, skipped, removed, or weakened.
+
+## CI integrity
+
+No workflow, lane, runner, coverage command, dependency installation path, or
+threshold changed.
+
+## Reviewer results
+
+Security, CI integrity, reuse/dedup, and docs pass after aligning the sole
+shared transitive mismatch. See `WS-QUAL-001-04P-internal-review-evidence.md`.
+
+## External review
+
+Three valid CodeRabbit findings were fixed and verified. See
+`WS-QUAL-001-04P-external-review-response.md`. Agent Gates passed on the prior
+head; exact rebased-head GitHub checks rerun after push.
+
+## Remaining risks
+
+04M must still prove mutmut behavior, target selection, result evidence, and
+hosted runtime. This manifest does not authorize or execute mutation testing.
+
+## Follow-up work
+
+After this PR merges, 04M still requires a separate human instruction.
+
+## Human review focus
+
+Confirm package selection, exact hashes, backend version alignment, and the
+protected-base consumption boundary.
+
+## Human merge ownership
+
+Only the user may approve and merge this PR.

scripts/mutation-requirements.in

@@ -0,0 +1,7 @@
+# Development/CI-only mutation engine. The compiled, hashed manifest is the
+# protected-main authority consumed by WS-QUAL-001-04M.
+mutmut==3.7.0
+# Keep the mutation runner aligned with the backend's tested toolchain.
+coverage==7.15.2
+packaging==26.2
+pytest==8.4.2