gitlore/plans/time-decay-expert-scoring.feedback-3.md

**Critical Plan Findings First**
1. The proposed index `idx_notes_mr_path_author ON notes(noteable_id, ...)` will fail: `notes.noteable_id` does not exist in schema (`migrations/002_issues.sql:74`).
2. Rename awareness is only applied in scoring queries, not in path resolution probes; today `build_path_query()` and `suffix_probe()` only inspect `position_new_path`/`new_path` (`src/cli/commands/who.rs:465`, `src/cli/commands/who.rs:591`), so old-path queries can still miss.
3. A fixed `"24m"` default window is brittle once half-lives become configurable; it can silently truncate meaningful history for larger half-lives.

Below are the revisions I’d make to your plan.

1. **Fix migration/index architecture (blocking correctness + perf)**
Rationale: prevents migration failure and aligns indexes to actual query shapes.
```diff
diff --git a/plan.md b/plan.md
@@ ### 6. Index Migration (db.rs)
- -- Support EXISTS subquery for reviewer participation check
- CREATE INDEX IF NOT EXISTS idx_notes_mr_path_author
-   ON notes(noteable_id, position_new_path, author_username)
-   WHERE note_type = 'DiffNote' AND is_system = 0;
+ -- Support reviewer participation joins (notes -> discussions -> MR)
+ CREATE INDEX IF NOT EXISTS idx_notes_diffnote_discussion_author_created
+   ON notes(discussion_id, author_username, created_at)
+   WHERE note_type = 'DiffNote' AND is_system = 0;
+
+ -- Path-first indexes for global and project-scoped path lookups
+ CREATE INDEX IF NOT EXISTS idx_mfc_new_path_project_mr
+   ON mr_file_changes(new_path, project_id, merge_request_id);
+ CREATE INDEX IF NOT EXISTS idx_mfc_old_path_project_mr
+   ON mr_file_changes(old_path, project_id, merge_request_id)
+   WHERE old_path IS NOT NULL;
@@
- -- Support state-aware timestamp selection
- CREATE INDEX IF NOT EXISTS idx_mr_state_timestamps
-   ON merge_requests(state, merged_at, closed_at, updated_at, created_at);
+ -- Removed: low-selectivity timestamp composite index; joins are MR-id driven.
```

2. **Restructure SQL around `matched_mrs` CTE instead of repeating OR path clauses**
Rationale: better index use, less duplicated logic, cleaner maintenance.
```diff
diff --git a/plan.md b/plan.md
@@ ### 3. SQL Restructure (who.rs)
- WITH raw AS (
-   -- 5 UNION ALL subqueries (signals 1, 2, 3, 4a, 4b)
- ),
+ WITH matched_notes AS (
+   -- DiffNotes matching new_path
+   ...
+   UNION ALL
+   -- DiffNotes matching old_path
+   ...
+ ),
+ matched_file_changes AS (
+   -- file changes matching new_path
+   ...
+   UNION ALL
+   -- file changes matching old_path
+   ...
+ ),
+ matched_mrs AS (
+   SELECT DISTINCT mr_id, project_id FROM matched_notes
+   UNION
+   SELECT DISTINCT mr_id, project_id FROM matched_file_changes
+ ),
+ raw AS (
+   -- signals sourced from matched_mrs + matched_notes
+ ),
```

3. **Replace correlated `EXISTS/NOT EXISTS` reviewer split with one precomputed participation set**
Rationale: same semantics, lower query cost, easier reasoning.
```diff
diff --git a/plan.md b/plan.md
@@ Signal 4 splits into two
- Signal 4a uses an EXISTS subquery ...
- Signal 4b uses NOT EXISTS ...
+ Build `reviewer_participation(mr_id, username)` once from matched DiffNotes.
+ Then classify `mr_reviewers` rows via LEFT JOIN:
+ - participated: `rp.username IS NOT NULL`
+ - assigned-only: `rp.username IS NULL`
+ This avoids correlated EXISTS scans per reviewer row.
```

4. **Make default `--since` derived from half-life + decay floor, not hardcoded 24m**
Rationale: remains mathematically consistent when config changes.
```diff
diff --git a/plan.md b/plan.md
@@ ### 1. ScoringConfig (config.rs)
+ pub decay_floor: f64, // default: 0.05
@@ ### 5. Default --since Change
- Expert mode: "6m" -> "24m"
+ Expert mode default window is computed:
+ default_since_days = ceil(max_half_life_days * log2(1.0 / decay_floor))
+ With defaults (max_half_life=180, floor=0.05), this is ~26 months.
+ CLI `--since` still overrides; `--all-history` still disables windowing.
```

5. **Use `log2(1+count)` for notes instead of `ln(1+count)`**
Rationale: keeps 1 note ~= 1 unit (with `note_bonus=1`) while preserving diminishing returns.
```diff
diff --git a/plan.md b/plan.md
@@ Scoring Formula
- note_contribution(mr) = note_bonus * ln(1 + note_count_in_mr) * 2^(-days_elapsed / note_half_life)
+ note_contribution(mr) = note_bonus * log2(1 + note_count_in_mr) * 2^(-days_elapsed / note_half_life)
```

6. **Guarantee deterministic float aggregation and expose `score_raw`**
Rationale: avoids hash-order drift and explainability mismatch vs rounded integer score.
```diff
diff --git a/plan.md b/plan.md
@@ ### 4. Rust-Side Aggregation (who.rs)
- HashMap<i64, ...>
+ BTreeMap<i64, ...> (or sort keys before accumulation) for deterministic summation order
+ Use compensated summation (Kahan/Neumaier) for stable f64 totals
@@
- Sort on raw `f64` score ... round only for display
+ Keep `score_raw` internally and expose when `--explain-score` is active.
+ `score` remains integer for backward compatibility.
```

7. **Extend rename awareness to query resolution (not only scoring)**
Rationale: fixes user-facing misses for old path input and suffix lookup.
```diff
diff --git a/plan.md b/plan.md
@@ Path rename awareness
- All signal subqueries match both old and new path columns
+ Also update `build_path_query()` probes and suffix probe:
+ - exact_exists: new_path OR old_path (notes + mr_file_changes)
+ - prefix_exists: new_path LIKE OR old_path LIKE
+ - suffix_probe: union of notes.position_new_path, notes.position_old_path,
+   mr_file_changes.new_path, mr_file_changes.old_path
```

8. **Tighten CLI/output contracts for new flags**
Rationale: avoids payload bloat/ambiguity and keeps robot clients stable.
```diff
diff --git a/plan.md b/plan.md
@@ ### 5b. Score Explainability via `--explain-score`
+ `--explain-score` conflicts with `--detail` (mutually exclusive)
+ `resolved_input` includes `as_of_ms`, `as_of_iso`, `scoring_model_version`
+ robot output includes `score_raw` and `components` only when explain is enabled
```

9. **Add confidence metadata (promote from rejected to accepted)**
Rationale: makes ranking more actionable and trustworthy with sparse evidence.
```diff
diff --git a/plan.md b/plan.md
@@ Rejected Ideas (with rationale)
- Confidence/coverage metadata: ... Deferred to avoid scope creep
+ Confidence/coverage metadata: ACCEPTED (minimal v1)
+ Add per-user `confidence: low|medium|high` based on evidence breadth + recency.
+ Keep implementation lightweight (no extra SQL pass).
```

10. **Upgrade test and verification scope to include query-plan and clock semantics**
Rationale: catches regressions your current tests won’t.
```diff
diff --git a/plan.md b/plan.md
@@ 8. New Tests (TDD)
+ test_old_path_probe_exact_and_prefix
+ test_suffix_probe_uses_old_path_sources
+ test_since_relative_to_as_of_clock
+ test_explain_and_detail_are_mutually_exclusive
+ test_null_timestamp_fallback_to_created_at
+ test_query_plan_uses_path_indexes (EXPLAIN QUERY PLAN)
@@ Verification
+ 7. EXPLAIN QUERY PLAN snapshots for expert query (exact + prefix) confirm index usage
```

If you want, I can produce a single consolidated “revision 3” plan document that fully merges all of the above into your original structure.