FABRIC/docs/schema.md

NeedleEvent Schema

schema-version: 1 — shared contract between NEEDLE and FABRIC.

Both projects must agree on this version. NEEDLE emits schema_version in its output; FABRIC asserts compatibility during parse via NEEDLE_EVENT_SCHEMA_VERSION in src/types.ts. If the values diverge, parseNeedleEvent throws.

Wire Format

Every event emitted by NEEDLE — over JSONL and OTLP logs — conforms to this shape:

{
  "schema_version": 1,
  "timestamp": "2026-04-21T11:20:19.962811515Z",
  "event_type": "worker.started",
  "worker_id": "tcb-alpha",
  "session_id": "d7261357",
  "sequence": 1,
  "bead_id": "bd-abc123",
  "data": {}
}

Fields

Field	Type	Required	Description
schema_version	number	recommended	Protocol version. Present in newer NEEDLE output; FABRIC asserts it when present.
timestamp	string	yes	RFC3339 timestamp. Display only — not authoritative for ordering.
event_type	string	yes	Taxonomy string from the event taxonomy table below.
worker_id	string	yes	Worker identifier (e.g. "tcb-alpha").
session_id	string	yes	Groups a worker's lifetime events into a single session.
sequence	number	yes	Per-worker monotonic counter. Authoritative for ordering within a worker.
bead_id	string	no	Present when the event pertains to a specific bead.
data	object	yes	Event-specific payload (see taxonomy table for notable fields). May be empty {}.

Ordering Contract

Sort events by (worker_id, sequence), not by timestamp.

Wall clocks skew across hosts. sequence is the worker's own monotonic counter and is the only reliable basis for replay and timeline reconstruction within a single worker. To interleave events from multiple workers, merge-sort on sequence within each worker_id partition, then order across partitions by timestamp as a tiebreaker.

Event Taxonomy

Format: category.action. Categories group related lifecycle phases.

Worker Lifecycle

event_type	Description	Notable data fields
worker.started	Worker boot	version, worker_name
worker.idle	Worker is idle, waiting for work	—
worker.stopped	Worker exit	reason
worker.draining	Worker is draining before shutdown	—

Bead Lifecycle

event_type	Description	Notable data fields
bead.claimed	Bead claim succeeded	bead_id
bead.prompt_built	Prompt constructed for agent	bead_id
bead.agent_started	Agent began working on bead	bead_id
bead.agent_completed	Agent finished working on bead	bead_id, duration_ms
bead.completed	Bead work fully completed	bead_id, duration_ms
bead.failed	Bead work failed	bead_id, error
bead.released	Bead released back to queue	bead_id
bead.claim_retry	Claim attempt will be retried	bead_id, attempt
bead.claim_exhausted	All claim retries exhausted	bead_id

Bead Mitosis

event_type	Description	Notable data fields
bead.mitosis.check	Checking if bead should split	bead_id
bead.mitosis.started	Mitosis began	bead_id
bead.mitosis.child_created	Child bead created	bead_id, child_id
bead.mitosis.complete	Mitosis finished	bead_id
bead.mitosis.failed	Mitosis failed	bead_id, error
bead.mitosis.skipped	Mitosis skipped (not needed)	bead_id

Strand Lifecycle

event_type	Description	Notable data fields
strand.started	Strand execution began	strand
strand.completed	Strand execution finished	strand, duration_ms
strand.fallthrough	Strand found no work	strand
strand.skipped	Strand was skipped	strand, reason

Hook Lifecycle

event_type	Description	Notable data fields
hook.started	Hook execution began	hook
hook.completed	Hook execution finished	hook, duration_ms
hook.failed	Hook execution failed	hook, error

Heartbeat

event_type	Description	Notable data fields
heartbeat.emitted	Periodic heartbeat	status
heartbeat.stuck_detected	Worker appears stuck	worker_id, since
heartbeat.recovery	Worker recovered from stuck state	worker_id

Mend (Maintenance)

event_type	Description	Notable data fields
mend.orphan_released	Orphaned bead released	bead_id
mend.heartbeat_cleaned	Stale heartbeat cleaned	worker_id
mend.logs_pruned	Old logs pruned	bytes_freed
mend.completed	Mend cycle finished	duration_ms

Unravel (Alternatives)

event_type	Description	Notable data fields
unravel.alternatives_created	Alternative beads created	parent_bead_id, count
unravel.alternative_created	Single alternative bead created	parent_bead_id, child_bead_id
unravel.analysis_started	Alternatives analysis began	bead_id
unravel.analysis_completed	Alternatives analysis finished	bead_id, duration_ms

Weave (Documentation Gaps)

event_type	Description	Notable data fields
weave.bead_created	Documentation gap bead created	bead_id, file, line
weave.analysis_started	Documentation analysis began	—
weave.analysis_completed	Documentation analysis finished	gaps_found, duration_ms

Pulse (Health Monitoring)

event_type	Description	Notable data fields
pulse.bead_created	Health issue bead created	bead_id, detector
pulse.scan_started	Health scan began	—
pulse.scan_completed	Health scan finished	issues_found, duration_ms
pulse.issue_detected	Specific issue found	detector, severity
pulse.detector_started	Individual detector started	detector
pulse.detector_completed	Individual detector finished	detector, duration_ms

Error Events

event_type	Description	Notable data fields
error.claim_failed	Bead claim failed	bead_id, error
error.agent_crash	Agent process crashed	bead_id, error, exit_code
error.timeout	Operation timed out	bead_id, duration_ms
error.release_failed	Bead release failed	bead_id, error

Effort & Budget

event_type	Description	Notable data fields
effort.recorded	Effort measurement recorded	bead_id, tokens, cost
budget.warning	Budget approaching limit	used, limit, percentage
budget.exceeded	Budget exceeded	used, limit
budget.per_bead_exceeded	Per-bead budget exceeded	bead_id, used, limit

File Locks

event_type	Description	Notable data fields
file.checkout	File checked out for editing	path
file.conflict	File conflict detected	path, workers
file.release	File lock released	path
file.stale	Stale file lock detected	path
lock.priority_bump	Lock priority bumped	path, worker_id
lock.priority_bump_received	Received priority bump notification	path, from_worker
lock.expired	Lock expired	path

TypeScript Reference

The canonical TypeScript definitions live in src/types.ts:

• NeedleEvent — the wire-schema interface
• NeedleEventType — union of all known event_type strings
• NEEDLE_EVENT_SCHEMA_VERSION — the current protocol version constant

The parser in src/parser.ts validates incoming events against the schema and throws on version mismatch. Legacy LogEvent is retained as an adapter for backward compatibility with existing UI consumers.