checkpoint

name	checkpoint
description	Write a timestamped mid-session checkpoint snapshot of decisions, progress, and next actions to .agents/checkpoints/, then link it from the active session log.
argument-hint	optional-short-label
allowed-tools	Bash(date:*), Bash(git branch:*), Bash(python3 -m json.tool:*), Bash(python3 scripts/redact_secrets.py:*), Glob, Read, Edit, Write
user-invocable	true

Checkpoint Command

Capture the current state of work as a durable, timestamped snapshot. Use this mid-session when you want a recoverable save point before a risky change, at the end of a working block, or whenever the user asks to "checkpoint" progress. The file is the human-readable record; the session log keeps a reference to it.

Optional label for this checkpoint: $ARGUMENTS

Triggers

Trigger	Effect
/checkpoint	Write a timestamped checkpoint and link it from the active session log.
/checkpoint label	Write a labeled checkpoint and link it from the active session log.

Process

Phase 1: Build checkpoint path

Resolve the timestamp, active session log, label, slug, and collision-safe checkpoint path.

Phase 2: Build and redact checkpoint

Render the checkpoint body and run it through the secret redactor before any Write call.

Phase 3: Persist and link

Write the redacted checkpoint to a path that does not already exist. Append checkpoint metadata to the active JSON session log when one exists, then validate the JSON.

Steps

1. Get the current UTC timestamp for the filename and the file body:

   date -u +%Y%m%d-%H%M%S
   

   Use the output as YYYYMMDD-HHMMSS. Also record the full ISO 8601 UTC time (date -u +%Y-%m-%dT%H:%M:%SZ) for the body.

2. Identify the active session log and default label:

   • Get the current branch with git branch --show-current.
   • Find .agents/sessions/*.json files and sort by filename descending. The filename order is the canonical "newest" order because session logs are named with YYYY-MM-DD-session-NN.
   • Read candidates in that order until you find the first log whose normalized session.branch equals the current branch. Normalize session.branch by trimming whitespace and removing one matching pair of surrounding backticks. That file is the active session log.
   • If $ARGUMENTS is empty after trimming, derive the label from the active session log's session.objective. If no active session log exists, derive it from the current branch. If that is empty, use checkpoint.

3. Build the filename slug from the label:

   • Lowercase the label, replace every run of non-alphanumeric characters with a single hyphen, and strip leading and trailing hyphens.
   • Truncate the slug to 40 characters.
   • Filename: CHECKPOINT-YYYYMMDD-HHMMSS-<slug>.md.
   • If slug generation returns an empty string, use checkpoint as the slug.

4. Select the checkpoint path. The directory already exists (tracked via .gitkeep). Do not overwrite an existing file. Use this collision loop before writing:

   • Start with CHECKPOINT-YYYYMMDD-HHMMSS-<slug>.md.
   • Check whether .agents/checkpoints/<candidate> already exists with Glob.
   • If it exists, try CHECKPOINT-YYYYMMDD-HHMMSS-<slug>-2.md, then -3, and continue until Glob returns no match.
   • Select the first path that does not already exist, but do not use Write yet.

5. Use this exact section structure. Fill each section from the current conversation and git state. Write "(none)" under a heading when a section has no content; never leave a heading empty.

   # Checkpoint YYYYMMDD-HHMMSS
   
   - Created: <ISO 8601 UTC>
   - Label: <the raw label, or "none">
   - Branch: <current git branch>
   
   ## Decisions
   
   Decisions made so far this session and the reasoning behind each.
   
   ## Completed
   
   Work finished and verified, with file paths or short commit SHAs (7-12
   characters) as evidence.
   
   ## Pending
   
   Work started but not finished, and work known to remain.
   
   ## Open Questions
   
   Unresolved questions, ambiguities, or blockers needing a human decision.
   
   ## Next Action
   
   The single next concrete step to take when work resumes.
   
   ## Context References
   
   Files, issues, PRs, ADRs, session logs, and memories a reader needs to resume.
   

6. Redact secrets before writing, then write the checkpoint. The checkpoint lands in git history; treat it as durable. Do not paste live credentials, tokens, or PII. Before using Write, run the checkpoint body through python3 scripts/redact_secrets.py and write the redacted output. If the redactor is unavailable or fails, stop and report the failure instead of writing unredacted durable text. Only after redaction succeeds, use Write on the collision-free path from step 4. Use short commit SHAs rather than full 40-character SHAs because the redactor masks long hex strings.

7. Link the checkpoint from the active session log:

   • If no active session log was found in step 2, report that no active session log was found. Do not invent or modify a log.
   • If the active session log exists, read the full original JSON first. Build the complete updated JSON in memory with a top-level checkpoints array. Create the array when it is absent. Append an object with path, created, label, and branch fields for this checkpoint.
   • Validate the complete updated JSON string before editing the file. Use a JSON parser that reads the full candidate from stdin, such as python3 -m json.tool. Never pass the JSON payload as a shell argument. If your harness cannot validate the candidate without writing a scratch file, leave the original session log unchanged and report that the session-log link was skipped.
   • Persist the updated JSON only after the validate-first step succeeds.
   • Run python3 -m json.tool <session-log-path> after editing. If JSON validation fails, report the failure and do not claim the checkpoint was linked from the session log.

8. Report the path you wrote, the session log path you updated or the reason no log was updated, and a one-line summary of what the checkpoint captured. Do not commit the file; leave that to the user or the session-end flow.

Verification

• Checkpoint file path did not already exist before Write.
• Checkpoint body was redacted with scripts/redact_secrets.py before Write.
• Active session log was updated, or the "no active session log" reason was reported.
• Updated session log JSON was validated before editing the original file.
• Updated session log passed python3 -m json.tool when a log was modified.

Anti-Patterns

• Do not overwrite an existing checkpoint path.
• Do not write unredacted durable text when the redactor fails.
• Do not create or guess a session log when no active branch-matching log exists.
• Do not edit a session log before validating the complete updated JSON string.
• Do not commit, push, or merge from this command.

Extension Points

• Add a restore command separately. Checkpoint only writes and links snapshots.
• Add automatic checkpointing separately. This command stays human-triggered.

This command writes a snapshot file and records a reference in the active session log when one exists. It does not push or commit. Keep it to the steps above.