fix(orchestration): persist linked pull requests#8689

Note

Fix Orchestrator.layer makeOrchestrator to persist linkedPullRequest

The makeOrchestrator function now includes linkedPullRequest in the built object when the command supplies it, including null to represent unlinking. When command.linkedPullRequest is undefined, the field is omitted from the payload. Adds a lifecycle test covering link, projection rebuild, and unlink flows in runtimeLayer.test.ts.

^{Macroscope summarized 1d9e754.}

Note

Low Risk Small, targeted decider fix with regression tests; no auth or broad behavioral changes beyond persisting an already-defined metadata field.

Overview Fixes a gap where thread.metadata.update accepted linkedPullRequest but the V2 orchestrator decider never applied it, so links never made it into thread state, events, or projections.

The thread.metadata.update handler in Orchestrator.ts now merges linkedPullRequest when the command sets it (including null to unlink), and omits the field when it is undefined, matching other optional metadata fields.

A runtime-layer test covers linking a PR, reading it from the thread projection and shell, surviving a projection rebuild, and unlinking via linkedPullRequest: null.

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