fix: exclude blank account_ref from engine preview aggregate (#93)

[agent-p1p]

Closes #93

Summary

group_engine_preview() (forensics/views.py) annotated account_ref=Min("account_ref"). Because account_ref is a blank-able CharField and the empty string sorts before any hex value, an engine with any event lacking an account_ref got "" from the aggregate — so the group-detail header engine chips rendered a blank account for an engine that actually has one. Meanwhile timeline_engines() (forensics/analysis.py:907) keeps the first non-empty account_ref, so the same engine showed its real account in the timeline column. The two paths disagreed.

The fix adds filter=~Q(account_ref="") to the aggregate so the preview reports a real account_ref whenever the engine has one, and falls back to "" (via the existing row["account_ref"] or "") only when every event for the engine is blank — exactly matching the timeline's first/any-non-empty semantics. Q was already imported.

Changes

• forensics/views.py — one-line aggregate change (+ explanatory comment).
• forensics/tests.py — two regression tests:
  • mixed present/absent account_ref for one engine -> preview reports the real ref
  • all-blank engine -> preview reports ""

Verification

Run locally with DJANGO_DEBUG=1:

• uv run ruff check . -> All checks passed
• uv run ruff format --check . -> 19 files already formatted
• uv run python manage.py test -> 149 tests OK (SQLite)
• RED/GREEN proof: the new mixed-engine test fails on the old Min("account_ref") (AssertionError: '' != 'aaaa...') and passes with the fix.

Pre-existing master breakage (NOT this PR)

master currently has a conflicting migration graph — two leaf nodes forensics/migrations/0007_add_auditevent_line_hash_engine_index (from #87) and 0007_auditfile_groups (from #80) both branch off 0006 with no merge migration. This makes manage.py test and makemigrations --check fail on master itself (master CI for #87 is red on the Run tests step). This PR's CI will be red for the same reason — it is unrelated to #93 and not introduced here. To run the suite locally I created a throwaway --merge migration, verified all 149 tests pass, then discarded it (not committed). The migration conflict needs a separate fix (a merge migration under the sensitive **/migrations/** path); it is intentionally out of scope for this display-correctness fix.

Sensitive paths

None touched. (forensics/views.py, forensics/tests.py only.)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 96e5eb39-4d82-4bb6-8dec-708396447aee

📥 Commits

Reviewing files that changed from the base of the PR and between 94630b0 and 042b805.

📒 Files selected for processing (2)

• forensics/tests.py
• forensics/views.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch pip/goggles-93

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[stage-review]

Ready to review this PR? Stage has broken it down into 2 individual chapters for you:

	Title
1	Exclude blank account_ref from engine preview aggregate
2	Add regression tests for engine preview account reporting

_{Chapters generated by Stage for commit 042b805 on Jun 22, 2026 12:28pm UTC.}

[agent-p1p]

Adversarial review: no PR-diff blockers

I reviewed PR #95 against issue #93.

Findings:

• Blocking: 0
• Suggestions: 0
• Nitpicks: 0

What I checked:

• group_engine_preview() now excludes blank account_ref values in the aggregate, so an engine with mixed blank/non-blank refs reports a real account ref instead of "".
• Existing all-blank behavior is preserved via the row["account_ref"] or "" fallback.
• Regression tests cover both mixed and all-blank engines.
• The PR diff only touches forensics/views.py and forensics/tests.py; no sensitive paths touched.

Local verification:

• uv run ruff check . -> pass
• uv run ruff format --check . -> pass
• Direct targeted Django tests currently fail before execution because master has a pre-existing divergent migration graph.
• With a reviewer-only temporary empty merge migration depending on both 0007 leaves, the two new targeted tests pass and the full suite passes: 149 tests OK.

CI note:

• Live CI is red on Django tests and checks for the same pre-existing migration conflict, not for this PR's account_ref change.
• Filed follow-up Add merge migration for divergent forensics 0007 migrations #96 to track that out-of-scope migration fix: Add merge migration for divergent forensics 0007 migrations #96
• Merge gate still must not auto-merge while CI is red. Marmots are particular about green lights.