Add Write Safety wiki page

Write-Safety.md

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+# Write Safety
+
+familiar began "read-only by design" and is now **read + write** — but writing is gated behind a single, deliberately strict safety layer. This page explains exactly when a write happens and what stops it.
+
+## The three conditions
+
+A write only happens when **all** of these hold:
+
+1. The tool is called with **`confirm=true`** (otherwise it returns a dry-run preview and changes nothing).
+2. Writes are **enabled globally** (on by default; opt out with `familiar writes disable`).
+3. The action runs through **`writes.guard`** — the single choke point every mutating tool must use.
+
+Every executed write is appended to an **audit log** on disk.
+
+## The gate: `writes.guard`
+
+[`writes.py`](https://git.hiddenden.cafe/Hiddenden/familiar/src/branch/main/src/familiar/writes.py) exposes one function that every write tool calls:
+
+```python
+async def guard(action, params, confirm, execute):
+    # confirm=False            -> dry-run preview, execute nothing
+    # confirm=True, writes off  -> raise WriteDisabled
+    # confirm=True, writes on   -> execute(), append to audit log, return result
+```
+
+### `confirm=false` → dry-run preview
+
+The default. Nothing is changed. The tool returns:
+
+```json
+{
+  "dry_run": true,
+  "action": "set_waypoint",
+  "params": { "...": "..." },
+  "note": "Nothing was changed. Pass confirm=true to execute (writes must be enabled)."
+}
+```
+
+This is how the AI can *show you what it would do* before you commit. You confirm by asking it to run the same action with `confirm=true`.
+
+### `confirm=true` but writes disabled → `WriteDisabled`
+
+If you've globally turned writes off, a confirmed write still does nothing and raises `WriteDisabled` telling you to run `familiar writes enable` to re-allow it.
+
+### `confirm=true` and writes enabled → execute + audit
+
+The action runs, and a line is appended to the audit log (see below).
+
+## The global toggle
+
+Writes are **on by default**. The toggle is controlled three ways, in precedence order:
+
+1. **Environment variable** `FAMILIAR_ENABLE_WRITES` — if set, it wins (`1/true/yes/on` = enabled).
+2. **On-disk flag file** `writes_disabled` in the data dir — created/removed by the CLI.
+3. **Default** — enabled (no flag file present).
+
+CLI:
+
+```bash
+uv run familiar writes            # show current state
+uv run familiar writes disable    # create the flag → block all writes
+uv run familiar writes enable     # remove the flag → re-allow writes
+```
+
+The `write_status` MCP tool reports the current state to the AI without touching the toggle.
+
+## The audit log
+
+Each executed write appends one JSON line to `audit.log` in the data dir:
+
+```json
+{"ts": 1719600000.0, "action": "send_mail", "params": { "...": "..." }}
+```
+
+Dry-runs and blocked (disabled) writes are **not** logged — only real, executed writes are. The log lives alongside the encrypted token store (see **[Configuration](Configuration)** for the path).
+
+## Which tools are writes?
+
+Every tool marked **WRITE** in the **[Tool Reference](Tool-Reference)**:
+
+- **Comms:** `send_mail`, `set_mail_read`, `respond_calendar_event`
+- **Contacts:** `add_contacts`, `remove_contacts`
+- **Fittings:** `create_fitting`, `delete_fitting`
+- **Fleet:** `invite_to_fleet`, `update_fleet`
+- **UI:** `set_waypoint`, `open_window`
+
+These are powered by the OAuth **write scopes** granted at login (see **[Authentication & Scopes](Authentication-and-Scopes)**).
+
+## For contributors
+
+When adding a write tool:
+
+- Give it a **required** `character` and a `confirm: bool = False` parameter.
+- Route the mutation through **`writes.guard`** — never call a mutating ESI endpoint directly.
+- Pass a clear `action` string and the user-facing `params` so the dry-run preview and audit line are meaningful.