Summarization fails silently after successful evolution — semantic commit message not generated

[yuujm87]

Description

After a successful evolution (installing starship via environment.systemPackages), the build check passed and the agent completed, but no semantic commit message was generated. The changeset was left uncommitted with committable: false.

Steps to Reproduce

1. Run an evolution: e.g. "install starship"
2. Agent completes all iterations, build check passes, narration shown
3. summarizing event fires ("Analyzing changes...")
4. Evolution result arrives with committable: false, groups: [], singles: [], and an entry in unsummarizedHashes

Expected Behavior

After a successful build and evolution, a semantic commit message should be generated and the changeset should be committable: true.

Actual Behavior

The changeMap in the result payload has:

{
  "groups": [],
  "singles": [],
  "unsummarizedHashes": ["e04ca0ca78b2bf008e5d2a2f85b52a3789d379e9c559402fb2b76a5161d961d3"]
}

The change exists in gitStatus (2 additions to modules/darwin/packages.nix), but ownSummaryId is null and currentChangesetId is null.

Environment

• nixmac version: darwin-system 26.11.57a3171
• macOS: macOS (Apple Silicon)
• Session timestamp: 2026-07-25T19:51–19:58 UTC
• Evolution iterations: 5, edits: 1, total tokens: 51,690
• SUMMARY_MODEL / SUMMARY_AI_PROVIDER: default (not overridden)

Session Telemetry

{
  "buildAttempts": 1,
  "durationMs": 439900,
  "editsCount": 1,
  "iterations": 5,
  "state": "generated",
  "thinkingCount": 1,
  "toolCallsCount": 7,
  "totalTokens": 51690
}

The summarizing event fired but the result shows no summaries were produced. No error was surfaced to the user — the failure was silent.

[linear-code]

ENG-604