docs(remediation): bank D-16 — local and CI test gates disagree by environment

Ran down Mos's flag. Both hypotheses were wrong: CI runs exactly 'pnpm test' (same
command, path IS exercised) and is green, while this host exits 97 on an
environment-dependent BASH_LINENO guard (#973) that aborts on bash 5.2.15 and not in
CI's container. PR #1027 touches zero files under packages/mosaic, so the guard is
genuinely pre-existing — f10-coder's report was accurate in every particular, and main
is equally affected here.

Not 'merges step around a red' but something worse in one respect: the local gate and
the CI gate disagree about what passing means. No agent on this host can get a green
pnpm test on any branch. A gate only CI can run cannot be a pre-push gate.

Second defect found while establishing this: in the main checkout the same package
fails differently (exit 1) because a test scans the working tree and picks up
apps/coordinator/venv third-party site-packages. A test whose verdict depends on
untracked files is not hermetic — same contamination source that broke format:check,
one foreign tree breaking two independent gates.

Coordinate with #1007/#1024 rather than opening a third lane.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/remediation/TASKS.md

@@ -93,6 +93,44 @@ and must not be cited as merge evidence. Rely on reviewer clearance + real CI.
 Three independent live instances in a single session — format gate, agent context reset, queue guard —
 is the class confirmed, not anecdote.
 
+### D-16 — the local test gate and the CI test gate disagree by environment
+
+Mos flagged a shape worth chasing: if `pnpm test` exits non-zero on a _pre-existing_ guard, then either
+`main` is red and merges step around it (the #868 shape again), or CI does not run that path. **Both
+branches turned out wrong, and the truth is a third thing.** Established by running it, not by asking:
+
+CI runs **exactly** `pnpm test` (`.woodpecker/ci.yml`, `test` step) — the same command. So the path _is_
+exercised. Yet:
+
+| environment               | result                                                                                                                                                                  |
+| ------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| CI container              | `test` step **green** (#2158, #2167)                                                                                                                                    |
+| this host, clean worktree | **exit 97** — `WAKE-ASSERT INIT ABORT: BASH_LINENO convention violated on bash 5.2.15(1)-release … expected [3 4], probe reported [3 5] (#973)`, after `PASS=18 FAIL=0` |
+| this host, main checkout  | **exit 1** — a _different_, second defect (below)                                                                                                                       |
+
+The guard is **environment-dependent**: it aborts on this host's bash and not in CI's container. `git
+diff origin/main...` confirms PR #1027 touches **zero** files under `packages/mosaic`, so the guard is
+genuinely pre-existing and unrelated — **f10-coder's report was accurate in every particular**, and
+`main` is equally affected on this host.
+
+**So it is not "merges step around a red" — it is worse in one specific way: the local gate and the CI
+gate do not agree about what passing means.** No agent on this host can obtain a green `pnpm test` at
+all, on any branch, including `main`. A gate an operator cannot run is a gate that only CI enforces,
+and a gate only CI enforces cannot be a pre-push gate. This is the hermeticity/portability class
+already live as #1007 (PR #1024).
+
+**Second, independent defect found while establishing the above.** In the main checkout the same
+package fails differently — exit 1 — because a test **scans the working tree** and asserts on files it
+finds, picking up `apps/coordinator/venv/**` (third-party `site-packages`: `pi = math.pi` in `rich`,
+`setuptools`, `mypy`). **A test whose result depends on untracked files present in the tree is not
+hermetic.** This is the _same_ contamination source that made `pnpm format:check` unpassable (D-1/D-7
+hygiene) — one untracked foreign tree silently breaking two independent gates.
+
+**Requirements.** RM-01/RM-04: a gate must produce the same verdict on a developer host and in CI, or
+declare loudly that it cannot run here — never diverge silently. RM-02 registers both as cases: the
+environment-divergence guard, and a hermeticity control asserting a suite's verdict is unchanged by the
+presence of untracked directories. Coordinate with #1007/#1024 rather than opening a third lane.
+
 ### D-15 — token scope is not repository permission (a THIRD capability layer)
 
 `f10-coder` was provisioned with `gitea-mosaicstack-f10-coder.token`, scopes `write:repository` +