docs: v0.23.0 agent-facing sweep — map, RAG corpus, CLAUDE.md (#468)

New map + RAG entries for the vault subsystem; sequence gate, lineage
merge, gate diff-base, CI guard, playwright MCP, dispatcher prefilter,
backup sidecar, and the 300/100 budget reflected across docs/map,
docs/rag, and CLAUDE.md; stale claims fixed (agent-ux 'no extra tools',
old budget defaults). No redirects needed — nothing publicly published
moved.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

docs/rag/workflows/task-claiming.md

@@ -29,10 +29,12 @@ The claim verb both claims and starts the task — there is no separate `start`
 
 Exactly one active WorkSession exists per task at a time (enforced in the service layer and by a DB unique index). A re-claim — pool release, reaper unclaim, escalation redirect — supersedes any prior agent's stale active session for that task and re-points the worktree at the new claim.
 
+If your task has `dependency_ids` in the same repo, the fresh branch cut also backfills each dependency's already-landed work when it sits outside your branch's own ancestor chain (a same-parent sibling or a same-project wave usually doesn't need this — the shared base already has it; a cross-subtree or cross-cell dependency edge can). This is a content assist, not a gate: a clean merge is silent, and a real conflict aborts the merge (your branch is left exactly at its cut point) and appends a note to the task naming the conflicting branch and files — resolve it by hand (merge the named branch into yours) before assembling your PR. A cross-repo dependency has no shared git history and is skipped entirely.
+
 ## Before Claiming
 
 1. Check you have capacity (developers / QA / documenters work one task at a time; **PM coordinators are exempt** — a Main / Cell PM may hold many roots at once, gated only by sequence dependencies)
-2. Verify dependencies are completed
+2. Verify dependencies are completed AND no lower-sequence sibling is still open (see Claiming Rules below)
 3. Read task description and acceptance criteria
 
 ## After Claiming
@@ -47,6 +49,7 @@ Exactly one active WorkSession exists per task at a time (enforced in the servic
 - **Self-review prevention**: QA cannot `claim_review` tasks they developed
 - **Self-documentation prevention**: Documenter cannot claim tasks they developed
 - **Branch requirement**: Branch auto-created on `i_will_work_on`
+- **Sequence order (strict, assignee-blind)**: if a task has a parent and a `sequence` number, it cannot be claimed while any sibling with a strictly lower sequence is still non-terminal — regardless of who owns which task. Siblings on the SAME sequence run in parallel (independent work ties at 0, or at the wave a delegating PM stamped from the collision graph). This is independent of, and stricter than, `dependency_ids`: a claim attempt on a sequence-held task fails even with no unmet dependency. The error names the blocking sibling by title — `unclaim`/wait is the only remedy, there is no override verb. The dispatcher pre-filters sequence-held (and dependency-held) tasks before attempting a claim, so you should rarely see this in practice — but a claim you make directly (rather than via `give_me_work`) can still hit it.
 
 ## Releasing a Claimed Task