quest: plan the land merge's lost content and the fixer's broken pipe

quest/m0/queue-watcher/base-merge-keeps.md

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+# [M] The tested-base merge keeps the base's content
+
+## Goal
+
+`mergeBase` (`src/cli/land.ts`) never removes content that both the PR head
+and the base still have. The commit it pushes to a PR's branch differs from
+the base only by the PR's own changes, plus the links it drops to quests the
+base finished. A test merges a base that finished one quest into a head that
+touches an unrelated README, and finds every other line of every quest file
+unchanged.
+
+## Plan
+
+Planned 2026-11-10 (maintainer, /quest-complete in moq-dev/moq). Milestone:
+✅ m0, in this epic (rejected: m0 standalone, m1), since it hit moq-dev/moq's
+queue today.
+
+On [moq-dev/moq#8429](https://github.com/moq-dev/moq/pull/8429), the bot's
+`quest land: merge tested base` commit `74d26316c6` has parents `8f0fee87e5`
+(the PR head) and `5e962fc7f1` (the base, on `main`). Against that base it
+deletes 669 lines in 45 files: every quest README's `## Required` list
+(`quest/README.md`, `quest/m0` through `quest/m5`, and epic READMEs), plus
+the PR's own changes. The head, the base, and their merge base `cd560bde5e`
+all have those lists, so no conflict explains it. The base had just finished
+one quest ([moq-dev/moq#8427](https://github.com/moq-dev/moq/pull/8427)
+deleted `quest/m0/nightly/qmux-bench-handshake.md`), so `prune` ran; it is
+the prime suspect, with the `quest resolve` merge driver next. Reproduce from
+those three commits before fixing.
+
+An iterating agent caught it by hand and restored `quest/` from `main`. A
+head like this one can otherwise land, since `quest check` passes on a tree
+whose READMEs list nothing.
+
+Public API: none. Wire: none.

quest/m0/queue-watcher/fixer-broken-pipe.md

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+# [S] The land fixer survives a closed pipe
+
+## Goal
+
+A fixer run on a dropped PR finishes with a fix, a flaky verdict, or a
+handback that names a decision, never a crash from a closed pipe. A test
+closes the reader of the step that crashed and finds the run still reports.
+
+## Plan
+
+Planned 2026-11-10 (maintainer, /quest-complete in moq-dev/moq). Milestone:
+✅ m0, in this epic (rejected: m0 standalone, m1).
+
+On moq-dev/moq the fixer handed back two ordinary drops with
+`fixer crashed (exit 1); run /quest-iterate` and the output
+`quest land check: [Errno 32] Broken pipe`:
+[moq-dev/moq#8406](https://github.com/moq-dev/moq/pull/8406) (a failed
+`merge_group` build, caused by a dead quest link) and
+[moq-dev/moq#8429](https://github.com/moq-dev/moq/pull/8429) (a merge
+conflict). Each then needed a person. `[Errno 32]` is Python's wording, so
+the crash may be in a script the fixer runs rather than in Quest's
+TypeScript; find which process prints it from the host's fixer logs first.
+If it is moq-dev/moq's own check script, fix it there instead (its
+`sh/migrate.sh` had the same `grep -q` under `pipefail` bug, fixed in
+[moq-dev/moq#8424](https://github.com/moq-dev/moq/pull/8424)) and delete
+this quest.
+
+Public API: none. Wire: none.