Signal Ckpt

⚡ signal-ckpt — Manual Checkpoint

Collapse the session into a ≤50 token state atom. Drop all prior history. Resume from the atom.

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Invocation Triggers

Activate when user says any of:

• /signal-ckpt
• "checkpoint", "compress context", "summarize session"
• "save state", "compress history", "ckpt"
• Auto-fires in SIGNAL-3 mode every 5 turns

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Output Format

CKPT[N]:
  §project={name} §stack={tech}
  progress=[{task}✓, {task}✗, {task}∅, {task}/]
  blockers=[{issue}⊥{component}]
  next={next_task}
  §decisions=[{decision}✓]

N = checkpoint sequence number, starting at 1. Increment on each checkpoint.

Minimal valid checkpoint (when session is simple):

CKPT[1]:
  §project=my-app
  progress=[auth✓, api/]
  next=finish api endpoints

Full checkpoint (active blockers, decisions, aliases):

CKPT[3]:
  §project=data-pipeline §stack=python+airflow
  [X1]=schema_validation_step [X2]=postgres_loader
  progress=[ingest✓, transform✓, X1✗, X2∅]
  blockers=[X1⊥schema_mismatch]
  next=fix schema_mismatch in X1
  §decisions=[use_upsert✓]

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Hard Rules

1. ≤50 tokens total. Count ruthlessly. If over, compress further: merge related tasks, abbreviate names, drop resolved items.

1. Checkpoint replaces conversation history. After this fires, all prior turns can be dropped. The checkpoint IS the history.

1. Only active blockers. Resolved blockers are gone. They do not appear anywhere in the checkpoint.

1. Only future-relevant decisions. §decisions only includes decisions that affect work not yet complete. Past decisions with no forward implication are dropped.

1. next is singular. One task. The most immediate pending action. Not a backlog.

1. Carry active aliases forward. Any [Xn] aliases still in use must appear in the checkpoint. Aliases for resolved items are dropped.

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Collapse Algorithm

When generating a checkpoint:

1. Identify all tasks mentioned in the session. Assign each a status from its last known state (✓ ✗ ∅ / ⊥).

1. Drop resolved blockers. If a blocker was fixed, it's gone.

1. Filter §decisions to only those that affect future work.

1. Set next to the single most immediate pending or in-progress action.

1. Count tokens. If >50:

• Merge related tasks (auth-login✓ + auth-refresh✓ → auth✓)
• Abbreviate task names (keep enough to be unambiguous)
• Drop sev1/low-signal completed tasks
• Omit §stack if obvious from project name

1. Verify sufficiency. Could someone read only this checkpoint and resume the work without prior context? If no, add the missing signal.

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Status Symbols

| Symbol | Meaning | |---|---| | ✓ | Complete | | ✗ | Failed / broken | | ∅ | Not started | | / | In progress | | ⊥ | Blocked |

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Resuming from a Checkpoint

When a session resumes after a checkpoint (new context window, continuation):

1. Paste the checkpoint as the first thing in the new context.
2. The checkpoint bootstraps full session state.
3. Resume from next without re-reading prior turns.
4. Aliases declared in the checkpoint are active immediately.

Resume format:

[Resuming from CKPT[2]]
CKPT[2]:
  §project=api-service §stack=node+express
  progress=[auth✓, routes/, tests∅]
  next=finish routes

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SIGNAL-3 Auto-Checkpoint

In SIGNAL-3 mode, checkpoints fire automatically every 5 turns (or the configured interval).

Auto-checkpoint behavior:

• Fires silently at the end of turn N (not announced before)
• Output appears as the last element of the turn N response
• Turn N+1 begins with the checkpoint already in context

Configuring the interval:

BOOT: CKPT:every 3 turns    ← more aggressive
BOOT: CKPT:every 10 turns   ← less aggressive
BOOT: CKPT:∅                ← disable auto-checkpoint (manual only)

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Examples

Simple 5-turn debug session

CKPT[1]:
  §project=auth-api
  progress=[login-endpoint✓, refresh-endpoint/, logout∅]
  blockers=[refresh⊥redis_timeout]
  next=fix redis timeout in refresh endpoint

Token count: ~22 tokens. Under limit.

Complex 15-turn architecture session

CKPT[3]:
  §project=platform-v2 §stack=nextjs+postgres+redis
  [X1]=auth_service [X2]=caching_layer [X3]=rate_limiter
  progress=[X1✓, X2/, X3∅, db-schema✓, api-routes/]
  blockers=[X2⊥session_store_conflict]
  next=resolve X2⊥session_store
  §decisions=[jwt_over_sessions✓, redis_for_X2✓]

Token count: ~38 tokens. Under limit.

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Eat Your Own Cooking

The checkpoint itself must be maximally compressed:

• No preamble ("Here is a checkpoint of our session:")
• No explanation after the checkpoint atom
• The checkpoint IS the output — nothing before, nothing after
• If something prevents checkpoint generation: one line, TMPL:bug format

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: mattbaconz
• Source: mattbaconz/signal
• License: MIT

Install and usage instructions live in the source repository linked above.