Resume (task checkpoint resume)¶

Audience: operators who killed an in-flight task (or had one crash) and want to pick up from the last successful step instead of restarting.

Overview¶

bernstein resume <task-id> loads the per-task checkpoint written by the orchestrator after every successful step transition, validates it, bumps resume_count, fires the task.resume lifecycle event, and hands control back so the orchestrator can re-spawn the task from the next step boundary.

v1 scope is local-only. Out of scope: cross-machine resume, distributed checkpoint storage, resuming across role-definition changes.

Source: src/bernstein/cli/commands/resume_cmd.py, src/bernstein/core/persistence/task_resume.py.

CLI¶

bernstein resume TASK_ID
  [--workdir DIR]   project root; defaults to cwd
  [--json]          emit machine-readable JSON instead of the Rich summary
  [--dry-run]       validate, bump resume_count, print plan; do not re-spawn

Re-spawn is dispatched by writing a signal file under .sdd/runtime/resume/. The worker watching that directory atomically claims it. If no worker is running, the signal persists until bernstein run starts and picks it up.

Exit codes¶

Code	Meaning
0	Resume prepared (and, unless `--dry-run`, dispatched)
2	No checkpoint on disk for `task_id`
3	Checkpoint corrupt or failed schema validation
4	`task.resume` lifecycle hook failed

Checkpoint layout¶

.sdd/runtime/checkpoints/<task-id>/checkpoint.json. Written atomically (tempfile -> os.replace -> fsync) after every successful step. Pydantic schema with extra="forbid" so any reader / writer drift fails fast.

Field	Use
`schema_version`	Forward-compat marker (v1)
`task_id`	Task this checkpoint belongs to
`last_completed_step_id`	Last step the orchestrator confirmed done; resume picks up at the next boundary
`trace_cursor`	Byte offset into `.sdd/traces/<task-id>.jsonl`
`scratchpad_path` / `scratchpad_sha256`	Pointer + content hash for recovered scratchpad
`adapter` / `adapter_session_id`	Adapter + session id captured at first spawn
`worktree_path`	Absolute path to preserved worktree
`resume_count`	Bumped by `bernstein resume` before re-spawn; dashboard flags flaky tasks
`merge_cursor`	Reserved for `core/streaming_merge.py` coordination
`meta`	Adapter-opaque k/v bag
`created_at` / `updated_at`	ISO-8601 UTC

Adapter capability matrix¶

Adapters that implement the resume() capability slot pick up the existing session. Adapters without resume() fall back to a fresh spawn with the recovered scratchpad re-injected as context. The capability matrix is at src/bernstein/adapters/_contract.py - resume_capability.

Examples¶

Dry-run a resume plan to inspect the recovery state:

bernstein resume task-9f3a --dry-run

Resume from a specific workdir (e.g. a fleet supervisor host):

bernstein resume task-9f3a --workdir /srv/bernstein/project-alpha

Resume and capture the plan for an automation:

bernstein resume task-9f3a --json > /tmp/resume-9f3a.json

Troubleshooting¶

No checkpoint: (exit 2). The task either never produced a checkpoint (no completed steps before the kill) or the checkpoint dir was wiped. The only recovery is a fresh run.

Corrupt checkpoint (exit 3). Schema validation failed; remove .sdd/runtime/checkpoints/<task-id>/checkpoint.json and run the task fresh, or fix the file by hand if you know what drifted.

Resume "dispatched" but nothing happens. No worker is consuming .sdd/runtime/resume/. Start bernstein run (or the relevant worker) and the signal will be claimed.