FN-8899: document unified AI merge path

Clarify that approved work is merged exclusively through the clean-room AI merge workflow.

- Replace the legacy merger entry point with runAiMerge in the architecture overview.
- Mark aiMergeTask as retained, soft-deprecated, and inert.

Files changed:
 docs/architecture.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Fusion-Task-Id: FN-8899

Fusion-Task-Lineage: 03436366-3f48-46c7-908e-ff97843b81d9

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

docs/architecture.md

@@ -627,7 +627,7 @@ See [Memory Plugin Contract](./memory-plugin-contract.md) for the full plan.
   <!-- FNXC:MergerUnification 2026-08-09-12:04: Master-plan U0 made clean-room `runAiMerge` the sole production merge path. The legacy `aiMergeTask` auto-prerebase policy is retained but inert, so executor reused-base refresh must not describe it as live merger behavior. -->
   - **Execution-only reused-base refresh (FN-8693):** planning creates isolated worktrees but does not refresh them; immediately before a graph `code` node, normal executor dispatch, or durable-agent heartbeat session, refresh-enabled reuse resolves the current integration target C1 and compares it with durable `task.baseCommitSha`. A clean no-own-commit checkout resets to C1; a clean own-commit checkout rebases and retains its resulting C2 `HEAD`, while storing C1—not C2—as the baseline. A durable C0/C1 mismatch is rechecked from git and durable metadata on every acquisition, so restart reconciliation needs no in-memory marker. Dirty, unresolved, unsupported worktrunk, git, conflict, persistence, and unprovable-reconciliation cases are typed non-execution outcomes that park before session start. If baseline persistence fails after git moves `HEAD`, the engine compensates to the original clean checkout and emits `worktree:base-refresh-persistence-failed-compensated`; otherwise it requires later proof-based reconciliation. Audit events are `worktree:base-refreshed`, `worktree:base-refresh-blocked`, `worktree:base-refresh-conflict`, `worktree:base-refresh-persistence-failed-compensated`, and `worktree:base-refresh-reconciled`. Plan/review/gate acquisition and merger acquisition remain excluded; production merger behavior is the unified clean-room `runAiMerge` path.
 - **Reviewer**: `reviewStep()` (`reviewer.ts`) performs plan/code/spec reviews
-- **Merger**: `aiMergeTask()` (`merger.ts`) merges approved work
+- **Merger**: `runAiMerge()` (`merge/merger-ai.ts`) is the sole production path that merges approved work; the retained `aiMergeTask()` body is soft-deprecated and inert.
 - **Task-detail chat / steering comments**: `TaskStore.addSteeringComment()` writes chat steering text to both `task.comments` and `task.steeringComments`. The executor still uses `steeringComments` for live in-session injection, while next-prompt agent lanes read canonical user-authored `task.comments`: planning/spec generation, spec review, plan/code reviewers, standard merger prompts, and clean-room AI merge + merge-review prompts all surface recent user comments through the shared `agent-user-comments.ts` formatter.
 
 #### Reviewer verdict recovery contract (FN-4092)