fix(#3786): authorize mutable scope from live observation only in the quick planner (#4005)

* test(#3786): the quick planner constraints must carry a mutable-scope authority rule

* fix(#3786): authorize mutable scope from live observation only in the quick planner

The quick planner could commit HISTORICAL scope as authorized edit or
verification scope before any live observation of the mutable state: a
minimized probe used cached PR-diff paths (65 of them, "pending
replacement") or broadened verification to the PR integration surface in
2 of 3 trials (#3786). One explicit authority requirement reduced that
to 0 of 3.

The new planner constraint authorizes mutable-state scope ONLY from a
live observation made at planning time (for conflict resolution, the
fresh merge index via git diff --name-only --diff-filter=U) or keeps
files/verify CONDITIONAL on it; historical STATE.md entries, recovery
notes, and cached PR/base diffs may guide investigation only. A
structural guard pins the rule in the shipped constraints block.

Emitted-Drift-Ack-Growth: quick.md — #3786: +620 bytes — one MUTABLE-SCOPE AUTHORITY constraint bullet added to the planner <constraints> block

* chore(#3786): changeset fragment (pr number backfilled after PR creation)

* chore(#3786): backfill changeset PR number (4005)

---------

Co-authored-by: sim <sim@local>

gsd-core/workflows/quick.md

@@ -315,6 +315,7 @@ ${AGENT_SKILLS_PLANNER}
 <constraints>
 - Create a SINGLE plan with 1-3 focused tasks
 - Quick tasks should be atomic and self-contained
+- MUTABLE-SCOPE AUTHORITY (#3786): when concrete edit or verification scope depends on mutable external state (a merge index, PR/base diffs, the working tree), authorize scope ONLY from a live observation made at planning time — for conflict resolution that is the fresh merge index via `git diff --name-only --diff-filter=U` — or keep `files`/`verify` CONDITIONAL on that observation. Historical STATE.md entries, recovery notes, and cached PR/base diff paths may guide investigation only; they are never edit or verification authority, and a plan must not enumerate them as authorized files "pending replacement".
 ${RESEARCH_MODE ? '- Research findings are available — use them to inform library/pattern choices' : '- No research phase'}
 ${VALIDATE_MODE ? '- Target ~40% context usage (structured for verification)' : '- Target ~30% context usage (simple, focused)'}
 ${VALIDATE_MODE ? '- MUST generate `must_haves` in plan frontmatter (truths, artifacts, key_links)' : ''}