test(analytics): gap-fill day-stack test picks the seeded day, not timeline[-1] (dev-ci red #3689)

[trinity-ability]

Why

dev-ci went red at aca0a01e (2026-10-14 00:17 UTC) on exactly one test out of 26,650: tests/unit/test_agent_analytics.py::TestTimelineGapFill::test_day_stacks_present_in_by_type — assert None == 1.

The test seeds three executions at _iso_ago(hours=1) and asserts they stack in out["timeline"][-1] (today). Between 00:00 and 01:00 UTC "an hour ago" is yesterday, so today's point is empty. It is wall-clock rot, not a regression: the test is unchanged since v0.7.0 (last touched by #1693), none of the five commits since dev-green touch analytics, and it reproduces locally on plain dev inside the window (3/3 runs) and passes outside it.

What

Select the timeline point whose date equals the seeded started_at[:10] instead of [-1]. Test-only change.

Verified

• Locally at 00:21 UTC (inside the failing window): tests/unit/test_agent_analytics.py 13 passed, twice.
• Merge-train attribution (P-20c): the red-dev issue is dev-ci red: Tier 2 failed on dev #3689; this PR is merged alone ahead of the 2026-10-14 train (refactor(a2a): every inbound A2A call needs a credential — drop the keyless trusted-network path; the trusted list becomes an outbound allowlist (ent#885) #3684, fix(resume): a resume turn no longer hands the agent the responder's email (ent#886) #3678, chore(enterprise): bump the submodule pointer to main (a52ba5c -> a5fdb07) #3687, feat(skill-gate): gate approvers by canon role — role:<id> beside the kinds (ent#848) #3686, fix(skill-gate): the person who asked sees how a gated request ended (#3653) #3657, fix: the Chat tab notice of a finished gated run quotes the run's reply (#3654) #3658).

Fixes #3689

🤖 Generated with Claude Code

[vybe]

merge-train (2026-10-14): red-dev fix for #3689 — wall-clock flake, test-only, reproduced inside the 00:00–01:00 UTC window and verified fixed there.