agent-capsule - SKILL.md Agent Skill

name: agent-capsule description: Use when an agent needs to install or use Agent Capsule to export, share, inspect, import, restore, or verify Codex and Claude Code session capsules, `.capsule.zip` files, or encrypted Agent Capsule links. Covers CLI setup, sender workflows, receiver bootstrap, approved import into local agent history, import-as-new semantics, secret-scan handling, and verification.

Agent Capsule

Overview

Agent Capsule is a CLI and capsule format for sharing coding agent sessions across machines or agent runtimes through capsule artifacts. Use this skill as the agent-facing operating guide; do not reimplement the capsule format in the prompt.

The CLI is the source of truth. A .capsule.zip or share link must remain self-bootstrapping for agents that do not have this skill installed.

CLI Setup

Check whether the CLI is available:

command -v capsule
capsule help

If the user asked to export, share, import, restore, inspect, or verify a capsule and the CLI is missing, install the latest released binary:

curl -fsSL https://raw.githubusercontent.com/z2z23n0/agent-capsule/main/install.sh | sh

This normal install path does not require Go. It downloads a platform archive from GitHub Releases, verifies checksums.txt, and installs capsule into ~/.local/bin unless INSTALL_DIR is set.

If the user explicitly asks to install from source for repository development, use Go:

go install github.com/z2z23n0/agent-capsule/cmd/capsule@main

If installation fails, report the exact blocker and do not invent a manual restore path.

Export Or Share

For a normal artifact handoff, export an encrypted share link. Codex remains the default source; pass --source claude for Claude Code:

capsule export --source codex --thread current
capsule export --source claude --thread current

Only when the user explicitly asks for a local file or zip capsule, add --format zip:

capsule export --source codex --thread current --format zip --name "<handoff topic>"
capsule export --source claude --thread current --format zip --name "<handoff topic>"

If the user provides a Worker or S3/R2 target, pass the matching capsule export flags instead of uploading the raw session yourself.

If artifact export fails with a secret-scan warning, stop and tell the user what was detected. Only rerun with --unsafe-include-secrets after explicit user approval. Secret scan covers session text, not OCR or image pixels, so remind the user to review screenshots and uploaded images when relevant.

Treat a full share URL containing #k=... as sensitive. The URL fragment is the decryption key.

Artifact Import Or Restore

Accept either a local .capsule.zip path or an encrypted share URL. If a link is missing #k=..., ask for the full link before importing.

For zip capsules, read the embedded agent instructions when useful:

unzip -p <file>.capsule.zip AGENT_README.md
unzip -p <file>.capsule.zip agent/restore.md

For local zip capsules, inspect first:

capsule inspect <file>.capsule.zip

For encrypted share links, the browser preview and manifest validate that the link shape is usable.

Import into the intended project directory after the user approves local agent history writes:

capsule import <file-or-url> --target codex --target-cwd . --execute
capsule import <file-or-url> --target claude --target-cwd . --execute

Agent Capsule import always creates a new native thread/session, like a session fork. Never design the workflow around replacing or overwriting the source thread/session, even when source and target use the same agent home.

Same-agent native import is raw-transcript lossless for the source runtime: Codex -> Codex restores a new Codex thread, and Claude -> Claude rewrites the Claude JSONL into a new sessionId under the target Claude project. Cross-agent artifact import preserves visible messages, tool evidence, working context, and a raw source sidecar under the target agent home.

Open Or Resume Result

When the user asks you to open, resume, or continue a capsule result, use the user's current agent surface when possible. Do not assume you are running in Codex; the current agent may be Codex, Claude Code, Cursor, OpenCode, or another agent.

flowchart TD
  A["Have capsule result or target session id"] --> B{"Current surface?"}
  B -->|App with thread tools| C["Use native app/thread tools"]
  C --> D["Pin, open, read, or continue target if supported"]
  D --> Z["Report verified result"]
  B -->|CLI / terminal| E["Infer host terminal"]
  E --> F{"Confident and controllable?"}
  F -->|Yes| G["Open a new tab/window in the same terminal"]
  F -->|No| H["Ask user or print exact command"]
  G --> Z
  H --> Z
  B -->|Unknown / remote / headless| I["Do not automate GUI"]
  I --> J["Print exact local command"]
  J --> Z

Prefer native app/thread tools over shell automation when available. For Codex App, useful tools may include set_thread_pinned, read_thread, and send_message_to_thread; pinning the target thread is preferred when direct opening is unavailable.

In CLI/TUI, do not run a nested resume command inline in the active agent session. Infer the host terminal from best-effort signals such as environment variables, parent process chain, running apps, or app-state tools. Treat this as heuristic, not ground truth; do not hard-code Terminal, Ghostty, iTerm2, Warp, WezTerm, Kitty, Alacritty, or any other terminal as the default.

If detection is uncertain or GUI control is unsafe, ask the user which surface to use, or print the exact command. Preserve the original model/provider when known. If the normal launcher is blocked by wrapper or updater behavior, use a direct installed binary only after confirming that blocker.

For Codex targets, the command shape is:

cd <cwd> && codex resume -m <model> <thread-id>

For Claude Code targets, the command shape is:

cd <cwd> && claude --session-id <session-id>

For other non-Codex targets, use that runtime's equivalent resume or open command. Claim success only after verifying through native app tools, terminal contents, or process inspection.

For Codex targets, verify thread existence with narrow checks such as session_index.jsonl, an exact session file path, or the specific resume process. Avoid broad recursive scans of CODEX_HOME; local Codex histories can be large and may include sensitive capsule URLs.

Verify

After an executed import, verify the new thread id from the import result:

capsule verify --target codex --home "${CODEX_HOME:-$HOME/.codex}" --thread <new-thread-id> --target-cwd .
capsule verify --target claude --home "${CLAUDE_CONFIG_DIR:-$HOME/.claude}" --thread <new-session-id> --target-cwd .

A capsule with safety.status = blocked can still be imported locally; treat it as a content warning that needs user awareness, not as a CLI runtime failure.

Boundaries

Do not migrate provider credentials, auth sessions, cloud state, API keys, filesystem checkpoints, or assume encrypted reasoning can be cryptographically continued in another runtime.

Do not write to local agent history without --execute and explicit user approval, except when the user has directly asked this agent to perform a local import and verification.