docs(remediation): bank D-31 — seat ran past 100% context with 28 uncommitted files

coder-mos1 hit 102.5%/372k on RM-03 with 28 modified files uncommitted and its branch
still at base — a full context window spent with nothing durable. Caught by polling seat
state, not by any system signal. Nothing warned anyone: no threshold alert, no
pre-compaction hook.

The founding failure mode of this mission — compaction destroying in-flight work —
nearly hit the mission's own delivery twice in one night. RM-01 survived because it had
committed work when checkpointed; this one had none. Commit-then-rotate works;
rotate-without-commit loses everything.

RM-34: a context threshold is not enough — rotation must force a durable checkpoint and
refuse to rotate a seat with uncommitted work. RM-50: seat context is observable state
and must be monitored; relying on an orchestrator to poll is instructions-not-enforcement
applied to lifecycle. Brief doctrine: commit early, commit WIP.

Adjacent: the diff spans 5 guides and 11 templates against a brief scoped to one script.
Queried, not assumed — but a 28-file diff from a one-script brief is a scope signal
regardless of the answer.

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

docs/remediation/TASKS.md

@@ -221,6 +221,38 @@ reviewer, and no other seat holds mosaicstack write. Flagged to the coordinator
 busy lane. Not blocking today — RM-02's code blockers are independently disqualifying — but the next
 otherwise-clean PR meets this.
 
+### D-31 — a seat ran past 100% context with 28 uncommitted files and no commits
+
+`coder-mos1` reached **102.5% / 372k context** on RM-03 with **28 modified files uncommitted** and its
+branch still at the base commit — i.e. **a full context window spent (~\$27) with nothing durable**. The
+orchestrator caught it by polling seat state, not by any signal from the system.
+
+**Nothing warned anyone.** No threshold alert, no pre-compaction hook, no "you are about to lose this"
+prompt. The seat did not report distress because from inside, running low on context feels like ordinary
+work right up until it is not. **The one failure mode the mission was founded on — compaction destroying
+in-flight work — very nearly happened to the mission's own delivery, twice in one night** (RM-01 was
+checkpointed at 69%; this one was already past the window).
+
+**What made RM-01 survivable and this one nearly not:** RM-01 had _committed_ work when it was
+checkpointed, so rotation was cheap. Here the work existed only in the worktree and the seat's context.
+**Commit-then-rotate works; rotate-without-commit loses everything.**
+
+**Requirements.**
+
+- **RM-34 (rotation daemon):** a context-threshold trigger is not enough — it must **force a durable
+  checkpoint before rotating**, and refuse to rotate a seat with uncommitted work until that work is
+  committed or explicitly discarded. Rotation without a commit is data loss with extra steps.
+- **RM-50 (fleet ownership):** seat context level is **observable state** and must be monitored, with a
+  threshold alert to the coordinator. Relying on an orchestrator to poll is exactly the "instructions,
+  not enforcement" pattern (D-4) applied to lifecycle.
+- **Worker briefs (immediate, mechanical):** _commit early, commit WIP, an imperfect commit that exists
+  beats perfect work that vanishes._ Added to standing brief doctrine rather than left to judgement.
+
+**Adjacent observation — scope drift, unverified.** The same diff spans 5 framework guides and 11 agent
+templates against a brief scoped to the queue guard and its tests. Queried rather than assumed: if the
+edits are consequential to the tri-state change they stay; if drive-by, they split. Recorded here because
+**a 28-file diff from a brief that named one script is a scope signal regardless of the answer.**
+
 ### D-29 — the registry's own coverage clause was SYNTACTIC, not semantic
 
 `rev-974` blocked PR #1030 with a finding that lands in the keystone's own enforcement: