feat(schema): Add migration 011 for resource events, entity references, and dependent fetch queue

Introduces five new tables that power temporal queries (timeline,
file-history, trace) via GitLab Resource Events APIs:

- resource_state_events: State transitions (opened/closed/reopened/merged/locked)
  with actor tracking, source commit, and source MR references
- resource_label_events: Label add/remove history per entity
- resource_milestone_events: Milestone assignment changes per entity
- entity_references: Cross-reference table (Gate 2 prep) linking
  source/target entity pairs with reference type and discovery method
- pending_dependent_fetches: Generic job queue for resource_events,
  mr_closes_issues, and mr_diffs with exponential backoff retry

All event tables enforce entity exclusivity via CHECK constraints
(exactly one of issue_id or merge_request_id must be non-NULL).
Deduplication handled via UNIQUE indexes on (gitlab_id, project_id).
FK cascades ensure cleanup when parent entities are removed.

The dependent fetch queue uses a UNIQUE constraint on
(project_id, entity_type, entity_iid, job_type) for idempotent
enqueue, with partial indexes optimizing claim and retry queries.

Registered as migration 011 in the embedded MIGRATIONS array in db.rs.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/011_resource_events.sql

@@ -0,0 +1,128 @@
+-- Migration 011: Resource event tables, entity references, and dependent fetch queue
+-- Powers temporal queries (timeline, file-history, trace) via GitLab Resource Events APIs.
+
+-- State change events (opened/closed/reopened/merged/locked)
+CREATE TABLE resource_state_events (
+    id INTEGER PRIMARY KEY,
+    gitlab_id INTEGER NOT NULL,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    issue_id INTEGER REFERENCES issues(id) ON DELETE CASCADE,
+    merge_request_id INTEGER REFERENCES merge_requests(id) ON DELETE CASCADE,
+    state TEXT NOT NULL,
+    actor_gitlab_id INTEGER,
+    actor_username TEXT,
+    created_at INTEGER NOT NULL,                -- ms epoch UTC
+    source_commit TEXT,
+    source_merge_request_iid INTEGER,           -- iid from source_merge_request ref
+    CHECK (
+        (issue_id IS NOT NULL AND merge_request_id IS NULL) OR
+        (issue_id IS NULL AND merge_request_id IS NOT NULL)
+    )
+);
+
+CREATE UNIQUE INDEX uq_state_events_gitlab ON resource_state_events(gitlab_id, project_id);
+CREATE INDEX idx_state_events_issue ON resource_state_events(issue_id) WHERE issue_id IS NOT NULL;
+CREATE INDEX idx_state_events_mr ON resource_state_events(merge_request_id) WHERE merge_request_id IS NOT NULL;
+CREATE INDEX idx_state_events_created ON resource_state_events(created_at);
+
+-- Label change events (add/remove)
+CREATE TABLE resource_label_events (
+    id INTEGER PRIMARY KEY,
+    gitlab_id INTEGER NOT NULL,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    issue_id INTEGER REFERENCES issues(id) ON DELETE CASCADE,
+    merge_request_id INTEGER REFERENCES merge_requests(id) ON DELETE CASCADE,
+    action TEXT NOT NULL CHECK (action IN ('add', 'remove')),
+    label_name TEXT NOT NULL,
+    actor_gitlab_id INTEGER,
+    actor_username TEXT,
+    created_at INTEGER NOT NULL,                -- ms epoch UTC
+    CHECK (
+        (issue_id IS NOT NULL AND merge_request_id IS NULL) OR
+        (issue_id IS NULL AND merge_request_id IS NOT NULL)
+    )
+);
+
+CREATE UNIQUE INDEX uq_label_events_gitlab ON resource_label_events(gitlab_id, project_id);
+CREATE INDEX idx_label_events_issue ON resource_label_events(issue_id) WHERE issue_id IS NOT NULL;
+CREATE INDEX idx_label_events_mr ON resource_label_events(merge_request_id) WHERE merge_request_id IS NOT NULL;
+CREATE INDEX idx_label_events_created ON resource_label_events(created_at);
+
+-- Milestone change events (add/remove)
+CREATE TABLE resource_milestone_events (
+    id INTEGER PRIMARY KEY,
+    gitlab_id INTEGER NOT NULL,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    issue_id INTEGER REFERENCES issues(id) ON DELETE CASCADE,
+    merge_request_id INTEGER REFERENCES merge_requests(id) ON DELETE CASCADE,
+    action TEXT NOT NULL CHECK (action IN ('add', 'remove')),
+    milestone_title TEXT NOT NULL,
+    milestone_id INTEGER,
+    actor_gitlab_id INTEGER,
+    actor_username TEXT,
+    created_at INTEGER NOT NULL,                -- ms epoch UTC
+    CHECK (
+        (issue_id IS NOT NULL AND merge_request_id IS NULL) OR
+        (issue_id IS NULL AND merge_request_id IS NOT NULL)
+    )
+);
+
+CREATE UNIQUE INDEX uq_milestone_events_gitlab ON resource_milestone_events(gitlab_id, project_id);
+CREATE INDEX idx_milestone_events_issue ON resource_milestone_events(issue_id) WHERE issue_id IS NOT NULL;
+CREATE INDEX idx_milestone_events_mr ON resource_milestone_events(merge_request_id) WHERE merge_request_id IS NOT NULL;
+CREATE INDEX idx_milestone_events_created ON resource_milestone_events(created_at);
+
+-- Cross-reference table (Gate 2): source/target entity pairs
+CREATE TABLE entity_references (
+    id INTEGER PRIMARY KEY,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    source_entity_type TEXT NOT NULL CHECK (source_entity_type IN ('issue', 'merge_request')),
+    source_entity_id INTEGER NOT NULL,          -- local DB id
+    target_entity_type TEXT NOT NULL CHECK (target_entity_type IN ('issue', 'merge_request')),
+    target_entity_id INTEGER,                   -- local DB id (NULL if unresolved)
+    target_project_path TEXT,                   -- for unresolved cross-project refs
+    target_entity_iid INTEGER,                  -- for unresolved refs
+    reference_type TEXT NOT NULL CHECK (reference_type IN ('closes', 'mentioned', 'related')),
+    source_method TEXT NOT NULL CHECK (source_method IN ('api', 'note_parse', 'description_parse')),
+    created_at INTEGER NOT NULL                 -- ms epoch UTC
+);
+
+CREATE UNIQUE INDEX uq_entity_refs ON entity_references(
+    project_id,
+    source_entity_type,
+    source_entity_id,
+    target_entity_type,
+    COALESCE(target_entity_id, -1),
+    COALESCE(target_project_path, ''),
+    COALESCE(target_entity_iid, -1),
+    reference_type,
+    source_method
+);
+
+CREATE INDEX idx_entity_refs_source ON entity_references(source_entity_type, source_entity_id);
+CREATE INDEX idx_entity_refs_target ON entity_references(target_entity_id) WHERE target_entity_id IS NOT NULL;
+CREATE INDEX idx_entity_refs_unresolved ON entity_references(target_project_path, target_entity_iid) WHERE target_entity_id IS NULL;
+
+-- Generic dependent fetch queue (resource_events, mr_closes_issues, mr_diffs)
+CREATE TABLE pending_dependent_fetches (
+    id INTEGER PRIMARY KEY,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    entity_type TEXT NOT NULL CHECK (entity_type IN ('issue', 'merge_request')),
+    entity_iid INTEGER NOT NULL,
+    entity_local_id INTEGER NOT NULL,
+    job_type TEXT NOT NULL CHECK (job_type IN ('resource_events', 'mr_closes_issues', 'mr_diffs')),
+    payload_json TEXT,                          -- optional extra data for the job
+    enqueued_at INTEGER NOT NULL,               -- ms epoch UTC
+    locked_at INTEGER,                          -- ms epoch UTC (NULL = available)
+    attempts INTEGER NOT NULL DEFAULT 0,
+    next_retry_at INTEGER,                      -- ms epoch UTC (NULL = no backoff)
+    last_error TEXT
+);
+
+CREATE UNIQUE INDEX uq_pending_fetches ON pending_dependent_fetches(project_id, entity_type, entity_iid, job_type);
+CREATE INDEX idx_pending_fetches_claimable ON pending_dependent_fetches(job_type, locked_at) WHERE locked_at IS NULL;
+CREATE INDEX idx_pending_fetches_retryable ON pending_dependent_fetches(next_retry_at) WHERE locked_at IS NULL AND next_retry_at IS NOT NULL;
+
+-- Update schema version
+INSERT INTO schema_version (version, applied_at, description)
+VALUES (11, strftime('%s', 'now') * 1000, 'Resource events, entity references, and dependent fetch queue');

src/core/db.rs

@@ -47,6 +47,10 @@ const MIGRATIONS: &[(&str, &str)] = &[
         "010",
         include_str!("../../migrations/010_chunk_config.sql"),
     ),
+    (
+        "011",
+        include_str!("../../migrations/011_resource_events.sql"),
+    ),
 ];
 
 /// Create a database connection with production-grade pragmas.