branch_groups.branchName is globally UNIQUE, but ensureBranchGroupForSource
only looked up an existing group by (sourceType, sourceId). When a second
mission's shared-branch triage resolved to a base branch (e.g. "main") that
another mission already owned a group for, createBranchGroup threw
"UNIQUE constraint failed: branch_groups.branchName". That error escaped
triageFeature and was swallowed by both callers (validation-failure
auto-triage and the reconcile sweep), leaving the mission's "defined"
features — including generated fix features — permanently un-triaged.
ensureBranchGroupForSource now reuses an existing open group for the same
branch name before attempting to create one, matching the established
getBranchGroupByBranchName(...) ?? ensureBranchGroupForSource(...) idiom.
Confirmed by reproducing against a snapshot of the affected mission DB:
triageFeature threw the UNIQUE error before, succeeds after.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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