storkit: create 445_bug_rate_limited_mergemaster_exits_advance_stories_to_done_without_merging

.storkit/work/1_backlog/445_bug_rate_limited_mergemaster_exits_advance_stories_to_done_without_merging.md

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+---
+name: "Rate-limited mergemaster exits advance stories to done without merging"
+---
+
+# Bug 445: Rate-limited mergemaster exits advance stories to done without merging
+
+## Description
+
+When the mergemaster agent is immediately rate-limited (zero turns, zero tool calls), it exits and run_server_owned_completion runs acceptance gates on the existing worktree. Since the coder already committed working code, the gates pass, and the pipeline advances the story to done — even though the mergemaster never executed run_squash_merge and the code was never cherry-picked onto master.
+
+## How to Reproduce
+
+Observed on stories 439 and 442. All mergemaster log entries show: init → rate_limit_event → error result. Zero turns, zero MCP tool calls, duration under 350ms. Yet both stories ended up in done with no merge commit on master.
+
+## Actual Result
+
+Stories advance to done with no code on master. The mergemaster never ran but the pipeline treated its exit as a successful completion.
+
+## Expected Result
+
+If the mergemaster exits without completing its work (no merge commit produced), the story should stay in the merge stage for retry, not advance to done.
+
+## Acceptance Criteria
+
+- [ ] run_server_owned_completion must not run for mergemaster agents — mergemaster has its own completion path via start_merge_agent_work
+- [ ] If the mergemaster process exits without producing a SquashMergeResult, the story stays in merge stage
+- [ ] Rate-limited mergemaster exits are treated as transient failures, not gate-passing completions
+- [ ] Story remains eligible for retry when mergemaster fails due to rate limiting