Pigeon

---
name: pigeon
description: "Inter-session pmail - send and receive messages between Claude Code sessions running in different project directories. Uses global SQLite database at ~/.claude/pmail.db. Triggers on: mail, pmail, send message, check mail, inbox, inter-session, message another session, pigeon."
license: MIT
allowed-tools: "Read Bash Grep"
metadata:
  author: claude-mods
  related-skills: sqlite-ops
---

# Pigeon

Inter-session messaging for Claude Code. Send and receive pmail between sessions running in different projects.

## Quick Reference

All commands go through `MAIL`, a shorthand for `bash "$HOME/.claude/pigeon/mail-db.sh"`.

Set this at the top of execution:

```bash
MAIL="$HOME/.claude/pigeon/mail-db.sh"
```

Then use it for all commands below.

## Command Router

Parse the user's input after `pigeon` (or `/pigeon`) and run the matching command:

| User says | Run |
|-----------|-----|
| `pigeon read` | `bash "$MAIL" read` |
| `pigeon read 42` | `bash "$MAIL" read 42` |
| `pigeon thread 42` | `bash "$MAIL" thread 42` (shows, does not mark read) |
| `pigeon send <project> "<subject>" "<body>"` | `bash "$MAIL" send "<project>" "<subject>" "<body>"` |
| `pigeon send --urgent <project> "<subject>" "<body>"` | `bash "$MAIL" send --urgent "<project>" "<subject>" "<body>"` |
| `pigeon send --attach <path> <project> "<subject>" "<body>"` | `bash "$MAIL" send --attach "<path>" "<project>" "<subject>" "<body>"` |
| `pigeon reply <id> "<body>"` | `bash "$MAIL" reply <id> "<body>"` |
| `pigeon reply --attach <path> <id> "<body>"` | `bash "$MAIL" reply --attach "<path>" <id> "<body>"` |
| `pigeon broadcast "<subject>" "<body>"` | `bash "$MAIL" broadcast "<subject>" "<body>"` |
| `pigeon search <keyword>` | `bash "$MAIL" search "<keyword>"` |
| `pigeon status` | `bash "$MAIL" status` |
| `pigeon unread` | `bash "$MAIL" unread` |
| `pigeon list` | `bash "$MAIL" list` |
| `pigeon list 50` | `bash "$MAIL" list 50` |
| `pigeon projects` | `bash "$MAIL" projects` |
| `pigeon clear` | `bash "$MAIL" clear` |
| `pigeon clear 7` | `bash "$MAIL" clear 7` |
| `pigeon alias <old> <new>` | `bash "$MAIL" alias "<old>" "<new>"` |
| `pigeon purge` | `bash "$MAIL" purge` |
| `pigeon purge --all` | `bash "$MAIL" purge --all` |
| `pigeon id` | `bash "$MAIL" id` |
| `pigeon migrate` | `bash "$MAIL" migrate` |
| `pigeon init` | `bash "$MAIL" init` |

When the user just says "check mail", "read mail", "inbox", "any mail?", or "any pmail?" - run `bash "$MAIL" read`.

When the user says "send mail to X", "send pmail to X", or "message X" - parse out the project name, subject, and body, then run `bash "$MAIL" send`.

## Project Identity

Each project gets a stable 6-character hash ID derived from its **git root commit** (the very first commit in the repo). This means:

- IDs survive directory renames, moves, and clones
- Case-insensitive filesystems (macOS) don't cause collisions
- Every clone of the same repo shares the same identity

For non-git directories, falls back to a hash of the canonical path (`pwd -P`).

A repo's git worktrees share its root commit, so they share its ID: every session in the repo, the main checkout and each lane alike, reads one inbox. See [Shared Inboxes](#shared-inboxes-worktrees).

Use `pigeon id` to see your project's name and hash:

```
claude-mods 7663d6
```

When sending messages, you can address projects by **name**, **hash**, or **path** - they all resolve to the same hash ID.

### Identicons

Each project hash renders as a unique pixel-art identicon (11x11 symmetric grid using Unicode half-block characters). Run `identicon.sh` to see yours, or view all projects with `pigeon projects`.

## Passive Notification (Hook)

A global PreToolUse hook checks for pmail on every tool call (no cooldown). Silent when inbox is empty. When mail is waiting it prints one JSON envelope, and Claude Code passes its `additionalContext` to the model:

```json
{"hookSpecificOutput":{"hookEventName":"PreToolUse","additionalContext":"=== INCOMING PMAIL (1 message(s)) ===\n..."}}
```

What the model reads:

```
=== INCOMING PMAIL (1 message(s)) ===

--- #42 from some-api (a1b2c3) @ 2026-09-30 10:12:04 ---
Subject: Auth endpoints ready
Login and refresh are live on staging.

=== ACTION REQUIRED: Inform the user about these messages and ask if they want to reply. ===
=== Then run: pigeon read (to mark as read) ===
=== To reply: pigeon reply <id> "message" ===
```

The JSON form is required. For PreToolUse, plain stdout goes to Claude Code's debug log and never reaches the model. Claude Code caps `additionalContext` at 10,000 chars, so the hook truncates message bodies at about 9,000 and points at `pigeon read`. The header and footer are always kept. Delivery does not mark mail read.

Each session is told about each message once. The signal file `/tmp/pigeon_signal_<hash>` is a timestamp that every send touches and nothing deletes. Each session keeps its own marker, `/tmp/pigeon_seen_<hash>_<session_id>`, holding the last message id it was shown. The fast path compares the two file times, so an empty inbox still costs one stat. The session id comes from the hook's stdin JSON; without one (a manual run), callers share an `anon` marker.

## Shared Inboxes (Worktrees)

Every session in a project reads one inbox, and a repo's worktrees are the same project. That is what makes lane-to-coordinator reporting work (`pigeon send claude-mods "READY lane/<x> <sha>"` from a lane reaches the session in the main checkout), and pigeon keeps it safe:

- **You are never handed your own mail.** Each message stores its sender's session (`CLAUDE_CODE_SESSION_ID`, the same id the hook gets). The hook and `read`, `count`, `unread` and `status` skip mail the calling session sent, so a lane's report waits for the others.
- **One session looking never hides mail from another.** Delivery is tracked per session (above). Earlier versions cleared the shared signal on delivery, so the lane that sent a report consumed the coordinator's wake-up.
- **Reading is still shared.** `pigeon read` marks mail read for the whole project. Inside a worktree the hook's footer says so: mark only mail meant for you, one at a time (`pigeon read <id>`); `pigeon thread <id>` shows a message without marking it.
- **Names can collide.** A name is a directory basename, so two repos can share one. Pigeon then warns on stderr, lists each candidate hash, and uses the sender's own project if it is one of them. Send by hash to choose (`pigeon projects` lists them).

## Attachments

Send file references with `--attach <path>` (repeatable). Paths are resolved to absolute and stored as references - files are not copied.

```bash
# Send with one attachment
pigeon send --attach src/config.ts my-api "Config update" "Updated the auth config"

# Send with multiple attachments
pigeon send --attach src/schema.sql --attach docs/API.md my-api "Schema + docs" "See attached"

# Reply with attachment
pigeon reply --attach output/report.json 42 "Here's the analysis"
```

Recipients see attachment paths with file sizes and can read them directly with the Read tool. If a file has been moved or deleted since sending, it shows as `(missing)`.

## When to Send

- You've completed work another session depends on
- An API contract or shared interface changed
- A shared branch (main) is broken or fixed
- You need input from a session working on a different project

## Per-Project Disable

```bash
touch .claude/pigeon.disable    # Disable hook notifications
rm .claude/pigeon.disable       # Re-enable
```

Only the hook is disabled - you can still send messages from the project.

---

## Installation

Pigeon requires two things: **scripts** (the mail engine) and a **hook** (passive notifications). Both install globally - one setup, every project gets pmail.

### Prerequisites

- `sqlite3` - ships with macOS, most Linux distros, and Git Bash on Windows. No install needed.
- `jq` - the hook uses it to build the JSON envelope Claude Code requires (`brew install jq`, `scoop install jq`, `apt install jq`). Without `jq` the hook stays silent, and `pigeon read` still works.

### Step 1: Copy Scripts

```bash
mkdir -p ~/.claude/pigeon
cp skills/pigeon/scripts/mail-db.sh ~/.claude/pigeon/
cp hooks/check-mail.sh ~/.claude/pigeon/
chmod +x ~/.claude/pigeon/mail-db.sh ~/.claude/pigeon/check-mail.sh
```

This gives you the pmail commands. You can now send and read messages manually:

```bash
bash ~/.claude/pigeon/mail-db.sh init      # Create database
bash ~/.claude/pigeon/mail-db.sh status    # Check it works
```

### Step 2: Enable the Hook

Add a `hooks` block to `~/.claude/settings.json`. This makes Claude check for pmail automatically on every tool call:

```json
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "*",
        "hooks": [
          {
            "type": "command",
            "command": "bash \"$HOME/.claude/pigeon/check-mail.sh\"",
            "timeout": 5
          }
        ]
      }
    ]
  }
}
```

**Important:** If you already have a `hooks` section in your settings, merge the PreToolUse entry into the existing array - don't replace the whole block.

Without this step, pigeon still works but you have to check manually (`pigeon read`). With the hook, unread pmail appears automatically.

### What Gets Created

```
~/.claude/
  settings.json            # Hook config (you edit this)
  pmail.db                 # Message store (auto-created on first use)
  pigeon/
    mail-db.sh             # All pmail commands (send, read, reply, etc.)
    check-mail.sh          # PreToolUse hook (silent when inbox empty)
```

### Verify

Run these in a terminal. Inside a Claude Code session, `read` skips mail that session sent, so a message to yourself stays unread.

```bash
# Check your project identity
bash ~/.claude/pigeon/mail-db.sh id

# Send yourself a test message (use your project name from above)
bash ~/.claude/pigeon/mail-db.sh send "my-project" "Test" "Hello from pigeon"

# Check it arrived
bash ~/.claude/pigeon/mail-db.sh read

# Clean up
bash ~/.claude/pigeon/mail-db.sh purge --all
```

### Uninstall

```bash
rm -rf ~/.claude/pigeon ~/.claude/pmail.db
# Then remove the hooks.PreToolUse entry from ~/.claude/settings.json
```

## Database

Single SQLite file at `~/.claude/pmail.db`. Auto-created on first `init` or `send`.

```sql
CREATE TABLE messages (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    from_project TEXT NOT NULL,   -- 6-char hash ID
    to_project TEXT NOT NULL,     -- 6-char hash ID
    subject TEXT DEFAULT '',
    body TEXT NOT NULL,
    timestamp TEXT DEFAULT (datetime('now')),
    read INTEGER DEFAULT 0,
    priority TEXT DEFAULT 'normal',
    thread_id INTEGER REFERENCES messages(id),
    attachments TEXT DEFAULT '',  -- newline-separated absolute paths
    from_session TEXT DEFAULT ''  -- sender's CLAUDE_CODE_SESSION_ID, '' outside a session
);

CREATE TABLE projects (
    hash TEXT PRIMARY KEY,        -- 6-char ID (git root commit or path hash)
    name TEXT NOT NULL,           -- Display name (basename of project dir)
    path TEXT NOT NULL,           -- Canonical path
    registered TEXT DEFAULT (datetime('now'))
);
```

## Troubleshooting

| Issue | Fix |
|-------|-----|
| `sqlite3: not found` | Ships with macOS, Linux, and Git Bash on Windows. Run `sqlite3 --version` to check. |
| Hook not firing | Ensure `hooks` block is in `~/.claude/settings.json` (Step 2 above) |
| Hook fires but no notification | Working as intended - hook is silent when inbox is empty |
| Mail is unread but Claude never mentions it | The hook must print JSON `additionalContext`, because plain PreToolUse stdout only reaches the debug log. Reinstall `check-mail.sh` from this repo and check `jq --version` |
| Messages not arriving | Target must be a known name, hash, or path. Use `pigeon projects` to see registered projects |
| A lane's report never reached the coordinator | Install the current `check-mail.sh` and `mail-db.sh` together. Older hooks cleared the shared signal when the lane saw its own report, and an older `read` marked it read |
| `Warning: 2 projects are named '...'` | Two directories share a basename. Send by the hash the warning lists |
| Upgraded from basename IDs | Run `pigeon migrate` to convert old messages to hash-based IDs |
| Changed display name | Use `pigeon alias old-name new-name` to update the project's display name |
| Want to disable for one project | `touch .claude/pigeon.disable` in that project's root |
| Check your project ID | Run `pigeon id` to see name and 6-char hash |