fix(desktop): key the change list on the channel, not the updater channel

[tusharbhardwaj-bk]

Follow-up to #120, which shipped the change list broken.

What happened

v0.0.34-staging-nightly.20260819.1 was built from the commit that added the change list, and published with no "What changed" section.

The previous-build lookup matched on the brand's updateChannel. That value is already staging-nightly, so the predicate searched tags for -staging-nightly-nightly. — a shape that does not exist. No previous tag, no commits, empty list.

It failed silently by design: the change list is deliberately never fatal, because a release that does not ship is an outage of the update channel while a release missing its notes is cosmetic. That was the right call and it is also what hid this — the release published normally and simply said nothing.

The fix

Key on the channel (staging / production), which is the same predicate the workflow's own already-published check uses:

select(.tag_name | contains("-${{ steps.channel.outputs.channel }}-nightly."))

The lookup moves into findPreviousChannelTag and is now covered. #120 tested the summariser and left this seam inline and untested — which is precisely where the bug was. The new tests use the real tag shapes, including one asserting a staging build never picks up the production channel's tag.

Verification

11 tests passed, tsgo --noEmit clean for scripts (0 errors), lint passes.

Merging this to expbkmain triggers the next staging release, whose body is the real proof — I'll check it rather than assume.

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	11.4 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	5.7 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	5.7 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	50.4 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	11	—	21	✅
Claude	Total thread wire	—	11.5 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	5.7 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	5.7 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	51.2 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	11	—	21	✅

Baseline: unavailable · PR result: 2c8719a · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 95.6 KiB
• Claude decoded thread snapshot: 96.3 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.