[P1] Diagnose DuckDB Today Picks query contract regressions

[fxbin]

Context

Bounded PostgreSQL full-suite diagnostic PR #34 exposed four consecutive failures in tests/test_duckdb_service.py while the surrounding DuckDB query tests continued to execute:

1. test_today_picks_query_uses_latest_analysis_only
2. test_today_picks_query_applies_aggregated_feedback
3. test_today_picks_query_uses_unified_risk_threshold_for_candidates
4. test_today_picks_query_excludes_ignored_content

Objective

Collect exact targeted tracebacks and determine whether this is:

• a stale SQL-contract regression test after a Today Picks query refactor;
• an actual production SQL/query regression;
• one shared root cause or multiple independent defects.

Required diagnostic pass

Run exactly these four tests with current dependencies and full tracebacks. For each failure record:

• assertion/exception;
• expected vs actual SQL/query contract;
• relevant current implementation path;
• whether surrounding digest/daily-report DuckDB query contracts remain valid;
• smallest durable repair boundary.

Decision rules

• Do not weaken candidate/risk/ignored-content semantics merely to satisfy stale string assertions.
• Do not rewrite production SQL until the current intended Today Picks product contract is identified from code/tests/callers.
• Group tests only when a shared root cause is demonstrated.

Acceptance criteria

• All four tests execute in a targeted diagnostic run with full failure evidence.
• Root cause is classified as stale test vs production regression.
• Any durable repair gets its own bounded Worker issue/branch when needed.
• Diagnostic workflow/PR is closed without merge.
• No process artifacts enter main.

Parent stabilization: #2
Regression inventory: #5

[fxbin]

Static triage update after repository Actions were intentionally paused:

• The four failing Today Picks tests all create their own in-memory DuckDB oltp_db.content_items table.
• None of those four fixture schemas defines content_type.
• Current production PicksMixin.query_today_picks() unconditionally selects c.content_type and optionally filters on it.
• content_type is a real durable schema field added by migration 20260812_0100_v2f3a4b5c6d7_add_content_type.py; this is not an accidental query-only field.

Therefore the highest-confidence root cause is stale test fixture schema, not simultaneous breakage of latest-analysis / feedback / risk-threshold / ignored-content semantics.

Because Actions are currently disabled, diagnostic PR #46 was closed before runtime traceback capture. Do not claim the traceback gate completed. The durable Worker should update only the four Today Picks in-memory schemas/inserts to include content_type (NULL is sufficient for these tests), leave production SQL unchanged, then run the exact four tests when a local/runtime environment with DuckDB is available.

Artifact boundary remains: no diagnostic workflow enters main.