docs: add per-note search PRD and user journey documentation

Per-note search PRD: Comprehensive product requirements for evolving
the search system from document-level to note-level granularity.
Includes 6 rounds of iterative feedback refining scope, ranking
strategy, migration path, and robot mode integration.

User journeys: Detailed walkthrough of 8 primary user workflows
covering issue triage, MR review lookup, code archaeology, expert
discovery, sync pipeline operation, and agent integration patterns.

docs/prd-per-note-search.feedback-1.md

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+Highest-impact gaps I see in the current plan:
+
+1. `for-issue` / `for-mr` filtering is ambiguous across projects and can return incorrect rows.
+2. `lore notes` has no pagination contract, so large exports and deterministic resumption are weak.
+3. Migration `022` is high-risk (table rebuild + FTS + junction tables) without explicit integrity gates.
+4. Note-doc freshness is incomplete for upstream note deletions and parent metadata changes (labels/title).
+
+Below are my best revisions, each with rationale and a git-diff-style plan edit.
+
+---
+
+1. **Add gated rollout + rollback controls**
+Rationale: You can still “ship together” while reducing blast radius. This makes recovery fast if note-doc generation causes DB/embedding pressure.
+
+```diff
+@@ ## Design
+-Two phases, shipped together as one feature:
++Two phases, shipped together as one feature, but with runtime gates:
++
++- `feature.notes_cli` (Phase 1 surface)
++- `feature.note_documents` (Phase 2 indexing/extraction path)
++
++Rollout order:
++1) Enable `notes_cli`
++2) Run note-doc backfill in bounded batches
++3) Enable `note_documents` for continuous updates
++
++Rollback:
++- Disabling `feature.note_documents` stops new note-doc generation without affecting issue/MR/discussion docs.
+```
+
+2. **Add keyset pagination + deterministic ordering**
+Rationale: Needed for year-long reviewer analysis and reliable “continue where I left off” behavior under concurrent updates.
+
+```diff
+@@ pub struct NoteListFilters<'a> {
+     pub limit: usize,
++    pub cursor: Option<&'a str>,        // keyset token "<sort_ms>:<id>"
++    pub include_total_count: bool,      // avoid COUNT(*) in hot paths
+@@
+-    pub sort: &'a str,                  // "created" (default) | "updated"
++    pub sort: &'a str,                  // "created" | "updated"
+@@ query_notes SQL
+-ORDER BY {sort_column} {order}
++ORDER BY {sort_column} {order}, n.id {order}
+ LIMIT ?
+```
+
+3. **Make `for-issue` / `for-mr` project-scoped**
+Rationale: IIDs are not globally unique. Requiring project avoids false positives and hard-to-debug cross-project leakage.
+
+```diff
+@@ pub struct NotesArgs {
+-    #[arg(long = "for-issue", help_heading = "Filters", conflicts_with = "for_mr")]
++    #[arg(long = "for-issue", help_heading = "Filters", conflicts_with = "for_mr", requires = "project")]
+     pub for_issue: Option<i64>,
+@@
+-    #[arg(long = "for-mr", help_heading = "Filters", conflicts_with = "for_issue")]
++    #[arg(long = "for-mr", help_heading = "Filters", conflicts_with = "for_issue", requires = "project")]
+     pub for_mr: Option<i64>,
+```
+
+4. **Upgrade path filtering semantics**
+Rationale: Review comments often reference renames/moves. Restricting to `position_new_path` misses relevant notes.
+
+```diff
+@@ pub struct NotesArgs {
+-    /// Filter by file path (trailing / for prefix match)
++    /// Filter by file path
+     #[arg(long, help_heading = "Filters")]
+     pub path: Option<String>,
++    /// Path mode: exact|prefix|glob
++    #[arg(long = "path-mode", value_parser = ["exact","prefix","glob"], default_value = "exact", help_heading = "Filters")]
++    pub path_mode: String,
++    /// Match against old path as well as new path
++    #[arg(long = "match-old-path", help_heading = "Filters")]
++    pub match_old_path: bool,
+@@ query_notes filter mappings
+-- `path` ... n.position_new_path ...
++- `path` applies to `n.position_new_path` and optionally `n.position_old_path`.
++- `glob` mode translates `*`/`?` to SQL LIKE with escaping.
+```
+
+5. **Add explicit performance indexes (new migration)**
+Rationale: `notes` becomes a first-class query surface; without indexes, filters degrade quickly at 10k+ note scale.
+
+```diff
+@@ ## Phase 1: `lore notes` Command
++### Work Chunk 1E: Query Performance Indexes
++**Files:** `migrations/023_notes_query_indexes.sql`, `src/core/db.rs`
++
++Add indexes:
++- `notes(project_id, created_at DESC, id DESC)`
++- `notes(author_username, created_at DESC, id DESC) WHERE is_system = 0`
++- `notes(discussion_id)`
++- `notes(position_new_path)`
++- `notes(position_old_path)`
++- `discussions(issue_id)`
++- `discussions(merge_request_id)`
+```
+
+6. **Harden migration 022 with transactional integrity checks**
+Rationale: This is the riskiest part of the plan. Add hard fail-fast checks so corruption cannot silently pass.
+
+```diff
+@@ ### Work Chunk 2A: Schema Migration (022)
++Migration safety requirements:
++- Execute in a single `BEGIN IMMEDIATE ... COMMIT` transaction.
++- Capture and compare pre/post row counts for `documents`, `document_labels`, `document_paths`, `dirty_sources`.
++- Run `PRAGMA foreign_key_check` and abort on any violation.
++- Run `PRAGMA integrity_check` and abort on non-`ok`.
++- Rebuild FTS and assert `documents_fts` rowcount equals `documents` rowcount.
+```
+
+7. **Add note deletion + parent-change propagation**
+Rationale: Current plan handles create/update ingestion but not all staleness paths. Without this, note documents drift.
+
+```diff
+@@ ## Phase 2: Per-Note Documents
++### Work Chunk 2G: Freshness Propagation
++**Files:** `src/ingestion/discussions.rs`, `src/ingestion/mr_discussions.rs`, `src/documents/regenerator.rs`
++
++Rules:
++- If a previously stored note is missing from upstream payload, delete local note row and enqueue `(note, id)` for document deletion.
++- When parent issue/MR title or labels change, enqueue descendant note docs dirty (notes inherit parent metadata).
++- Keep idempotent behavior for repeated syncs.
+```
+
+8. **Separate FTS coverage from embedding coverage**
+Rationale: Biggest cost/perf risk is embeddings. Index all notes in FTS, but embed selectively with policy knobs.
+
+```diff
+@@ ## Estimated Document Volume Impact
+-FTS5 handles this comfortably. Embedding generation time scales linearly (~4x increase).
++FTS5 handles this comfortably. Embedding generation is policy-controlled:
++- FTS: index all non-system note docs
++- Embeddings default: only notes with body length >= 40 chars (configurable)
++- Add config: `documents.note_embeddings.min_chars`, `documents.note_embeddings.enabled`
++- Prioritize unresolved DiffNotes before other notes during embedding backfill
+```
+
+9. **Bring structured reviewer profiling into scope (not narrative reporting)**
+Rationale: This directly serves the stated use case and makes the feature compelling immediately.
+
+```diff
+@@ ## Non-Goals
+-- Adding a "reviewer profile" report command (that's a downstream use case built on this infrastructure)
++- Generating free-form narrative reviewer reports.
++  A structured profiling command is in scope.
++
++## Phase 3: Structured Reviewer Profiling
++Add `lore notes profile --author <user> --since <window>` returning:
++- top commented paths
++- top parent labels
++- unresolved-comment ratio
++- note-type distribution
++- median comment length
+```
+
+10. **Add operational SLOs + robot-mode status for note pipeline**
+Rationale: Reliability improves when regressions are observable, not inferred from failures.
+
+```diff
+@@ ## Verification Checklist
++Operational checks:
++- `lore -J stats` includes per-`source_type` document counts (including `note`)
++- Add queue lag metrics: oldest dirty note age, retry backlog size
++- Add extraction error breakdown by `source_type`
++- Add smoke assertion: disabling `feature.note_documents` leaves other source regeneration unaffected
+```
+
+---
+
+If you want, I can produce a single consolidated revised PRD draft (fully merged text, not just diffs) as the next step.