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3fbbaab | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 | # Change-triggered backup — hook install
One page on wiring the `backup_on_change.py` PostToolUse hook into Claude
Code so a new snapshot fires automatically whenever you edit a tracked
config file (`~/.claude/settings.json`, agents, skills, top-level
manifests, etc.).
## What it does
On every `Edit` / `Write` / `MultiEdit` tool call, the hook:
1. Reads the tool payload from stdin.
2. Resolves `tool_input.file_path` and checks if it sits under
`~/.claude` in a file/tree/memory path tracked by `BackupConfig`.
3. If tracked, shells out to
`python <repo>/src/backup_mirror.py snapshot-if-changed --reason <tool>:<basename>`.
4. `snapshot-if-changed` hashes every tracked file, compares against the
most recent snapshot's `manifest.json`, and only creates a new folder
when at least one SHA differs.
No-op edits don't create folders. The hook always exits 0 so a bug in
the backup layer cannot stall a Claude session.
## Register the hook
Edit `~/.claude/settings.json` and add the following under `hooks` (keep
any existing entries alongside it). Replace `<REPO>` with the absolute
path to this checkout — on Windows this is a path like
`C:/Steves_Files/Work/Research_and_Papers/ctx`.
```json
{
"hooks": {
"PostToolUse": [
{
"matcher": "Edit|Write|MultiEdit",
"hooks": [
{
"type": "command",
"command": "python <REPO>/hooks/backup_on_change.py"
}
]
}
]
}
}
```
Notes:
- The `matcher` is a regex against the tool name — the three names above
are the only tools that touch files.
- Use forward slashes in the path even on Windows.
- If `python` on your PATH is not the interpreter you want, give the
absolute path instead (e.g.
`C:/Users/you/.pyenv/pyenv-win/versions/3.13.2/python.exe`).
## Verify it works
1. Reload Claude Code (the hook registration is read at session start).
2. Edit a tracked file, e.g. `~/.claude/CLAUDE.md`.
3. Watch `~/.claude/backups/` — a new folder named
`<timestamp>__edit-claude-md` should appear within a second.
4. Edit the same file again with identical content — no new folder
appears (SHA is unchanged).
If nothing shows up, run the verb manually to isolate the failure:
```bash
python -m backup_mirror snapshot-if-changed --reason smoke-test --json
```
The JSON output tells you which files the detector considered new,
changed, or removed.
## What gets backed up
See `src/backup_config.py` and the `backup` section of
`src/config.json` for the current defaults:
- **top_files** — `settings.json`, `skill-manifest.json`,
`pending-skills.json`, `CLAUDE.md`, `AGENTS.md`, `user-profile.json`,
`skill-system-config.json`, `skill-registry.json`.
- **trees** — `agents/`, `skills/`.
- **memory** — `projects/*/memory/**` when `memory_glob` is true.
- **always excluded** — `.credentials.json`, `claude.json`, token
caches; these are dropped even if a user config lists them.
To override per user, drop a partial config at
`~/.claude/backup-config.json`. Fields you omit fall back to the repo
default. Example:
```json
{
"retention": { "keep_latest": 100 },
"top_files": ["settings.json", "CLAUDE.md"]
}
```
## Manual CLI
The same verb is available as a one-shot command:
```bash
# snapshot only when something changed
python -m backup_mirror snapshot-if-changed --reason manual-check
# force an unconditional snapshot with a reason label
python -m backup_mirror create --reason pre-upgrade
```
Both land under `~/.claude/backups/<timestamp>__<reason>/` and write a
`manifest.json` that records the reason alongside every file's SHA-256.
## Watchdog — snapshot on changes outside a Claude session
The PostToolUse hook only fires on `Edit` / `Write` / `MultiEdit` tool
calls *inside* a Claude session. If you edit `~/.claude/settings.json`
in VS Code, or a `git pull` updates an agent file, the hook never
sees it.
For that gap, run the polling watchdog — a simple loop that calls
`snapshot-if-changed` every N seconds:
```bash
python -m backup_mirror watchdog --interval 60
```
Flags:
| Flag | Meaning |
| --- | --- |
| `--interval N` | Seconds between polls. Clamped to `[5, 3600]`. Default 60. |
| `--reason-prefix LBL` | Prefix used for each snapshot's `--reason` label. Default `watchdog`. |
| `--once` | Run exactly one tick and exit. Useful for cron / Task Scheduler. |
| `--json` | Emit run stats as JSON on exit. |
Because change detection is SHA-gated, polling is cheap — a tick with
no real changes does zero disk writes.
### Running it as a background service
Ready-to-use service manifests live under
[`docs/services/`](https://github.com/stevesolun/ctx/tree/main/docs/services).
Each one expects you to edit a handful of paths — there's no installer
that guesses where you keep the checkout.
- **Linux (systemd user unit)** —
[`docs/services/systemd/claude-backup-watchdog.service`](https://github.com/stevesolun/ctx/blob/main/docs/services/systemd/claude-backup-watchdog.service).
Copy to `~/.config/systemd/user/`, set `CTX_REPO`, then
`systemctl --user enable --now claude-backup-watchdog.service`.
- **macOS (launchd agent)** —
[`docs/services/macos/com.claude.backup.watchdog.plist`](https://github.com/stevesolun/ctx/blob/main/docs/services/macos/com.claude.backup.watchdog.plist).
Edit the `ProgramArguments` paths, drop into
`~/Library/LaunchAgents/`, then
`launchctl load -w ~/Library/LaunchAgents/com.claude.backup.watchdog.plist`.
- **Windows (Task Scheduler installer)** —
[`docs/services/windows/install-backup-watchdog.ps1`](https://github.com/stevesolun/ctx/blob/main/docs/services/windows/install-backup-watchdog.ps1).
Run `pwsh -File docs/services/windows/install-backup-watchdog.ps1`
from the repo root; it detects Python on PATH, registers a
`ClaudeBackupWatchdog` scheduled task that runs at logon, and kicks
off the first tick. `-Uninstall` removes it.
All three manifests assume the watchdog runs as an **unprivileged
user** — no admin/root — because it only reads `~/.claude/` and writes
`~/.claude/backups/`.
The watchdog stops cleanly on SIGINT/SIGTERM, flushes its stats line
to stderr, and exits 0. Pair it with the hook: the hook handles
in-session edits in real time; the watchdog catches everything else.
## Retention — how old snapshots get pruned
Auto-pruning runs after every successful `snapshot-if-changed`, so the
hook cannot fill the disk. The active policy comes from
`BackupRetention` in `src/backup_config.py` (or your user override):
| Field | Default | Meaning |
| --- | --- | --- |
| `keep_latest` | `50` | Always keep the N most-recent snapshots. |
| `keep_daily` | `14` | For the M most-recent UTC days that have snapshots, keep the newest snapshot from each. |
A snapshot survives the sweep iff it's in the **union** of those two
sets. Snapshots whose `manifest.json` has a missing or zero
`created_at` are always protected — we never silently delete something
we can't place in time.
To override per user, add a partial config at
`~/.claude/backup-config.json`:
```json
{
"retention": { "keep_latest": 100, "keep_daily": 30 }
}
```
### Manual prune
```bash
# Dry-run the configured policy — no deletions, JSON report.
python -m backup_mirror prune --policy --dry-run --json
# Apply the configured policy for real.
python -m backup_mirror prune --policy
# Legacy mode (still works): keep only the N newest.
python -m backup_mirror prune --keep 20
```
The policy output tells you which snapshots were kept by `keep_latest`
versus `keep_daily`, so a surprising retention decision is easy to
audit.
## Troubleshooting
| Symptom | Likely cause |
| --- | --- |
| Hook never fires | Settings not reloaded, or `matcher` typo. |
| Snapshot folder with no `reason` suffix | Called `create` without `--reason`. |
| Hook fires but no folder appears | Content hash matched — nothing actually changed. |
| Credentials appear in a snapshot | User put them in `top_files`; the `ALWAYS_EXCLUDE` filter would drop them — check you're on the current `backup_config.py`. |
| `ImportError: backup_config` from the hook | Repo moved; update the path in `settings.json`. |
| Snapshots pile up forever | `retention.keep_latest` / `keep_daily` too high. Run `prune --policy --dry-run --json` to see what the current policy would do, then lower the caps in `~/.claude/backup-config.json`. |
| Prune removed too much | Run `prune --policy --dry-run` *before* committing to a new policy. A snapshot with a missing/zero `created_at` is always protected, so if it's getting deleted the manifest is probably fine and the policy is genuinely too aggressive. |
|