TLDR;
The philosophy of CLI usage is "fire and forget" and "best effort". You
can opt out by setting `ARCADE_USAGE_TRACKING=0`.
We are capturing two events: `CLI execution succeeded` and `CLI
execution failed`. Reporting to PostHog is a short lived (maximum 10
seconds) subprocess that does not block the main CLI execution process.
`~/.arcade/usage.json` persists two values `anon_id` and
`linked_principal_id`. The logged in status of the CLI user determines
which ID is used. Upon `arcade login`, the `anon_id` is aliased with
`linked_principal_id`. Upon `arcade logout` the `linked_principal_id` is
removed and the `anon_id` is rotated.
## CLI Usage Tracking - How It Works
The usage tracking system implements an identity management and event
tracking pipeline. Here's how the pieces work together:
### **Identity State Management (`usage.json`)**
The system maintains a persistent identity file at
`~/.arcade/usage.json` with this structure:
```json
{
"anon_id": "uuid",
"linked_principal_id": "uuid" | null
}
```
**Key mechanics:**
- **`anon_id`**: Generated once on first CLI use and persists across
sessions. This UUID tracks all anonymous activity.
- **`linked_principal_id`**: Initially `null`. Once the user logs in and
we successfully alias their identity, this field stores their
`principal_id` to indicate this `anon_id` has been linked.
- **Atomic writes**: All updates use a temp file + atomic rename pattern
to prevent corruption from concurrent CLI processes
- **File locking**: Uses `fcntl` (Unix) to coordinate reads/writes
across multiple simultaneous CLI invocations
- **In-memory cache**: The `UsageIdentity` class caches the loaded data
to avoid repeated file I/O within a single CLI invocation
### **Identity Resolution Flow**
When tracking an event, the system determines the `distinct_id` (who to
attribute the event to) via this waterfall:
1. **Check `linked_principal_id`** in `usage.json`
- If present → use it (user was previously aliased)
- This is the fastest path and avoids API calls
2. **Fetch `principal_id` from Arcade Cloud API**
- Makes HTTP request to `/api/v1/auth/validate` with the user's API key
from `~/.arcade/credentials.yaml`
- If authenticated → returns `principal_id`
- Has 2s timeout for responsiveness
3. **Fall back to `anon_id`**
- If not authenticated or API call fails → use anonymous ID
- Marks event with `is_anon=True` flag
### **The Aliasing Lifecycle**
PostHog aliasing links anonymous activity to authenticated users. Here's
the state machine:
#### **Stage 1: Anonymous User**
```
usage.json: { "anon_id": "abc-123", "linked_principal_id": null }
All events → sent with distinct_id="abc-123" and is_anon=True
```
#### **Stage 2: Login Event**
1. User runs `arcade login`
2. Command completes successfully (auth token saved)
3. `CommandTracker` detects successful login
4. Fetches `principal_id` from API
5. Checks `should_alias()` → returns `True` because
`linked_principal_id` is `null`
6. **Calls `alias()` synchronously** (blocking):
```python
posthog.alias(previous_id="abc-123", distinct_id="zyx-321")
```
7. Updates `usage.json`:
```json
{ "anon_id": "abc-123", "linked_principal_id": "zyx-321" }
```
8. PostHog backend merges all events with `distinct_id="abc-123"` into
the user profile for `"zyx-321"`
#### **Stage 3: Authenticated User**
```
usage.json: { "anon_id": "abc-123", "linked_principal_id": "zyx-321" }
All events → sent with distinct_id="zyx-321" and is_anon=False
```
- Events are directly attributed to the authenticated user
- No more API calls needed (uses cached `linked_principal_id`)
#### **Stage 4: Logout Event**
1. User runs `arcade logout`
2. Logout event is sent with the authenticated `distinct_id`
3. `CommandTracker` detects successful logout
4. **Rotates identity** by calling `reset_to_anonymous()`:
```json
{ "anon_id": "xyz-789", "linked_principal_id": null }
```
5. New `anon_id` prevents cross-contamination if another user logs in
### **Critical Constraint: Alias Timing**
PostHog requires that `alias()` is called **BEFORE** any events are sent
with the new `distinct_id`. This is why:
- **`alias()` is synchronous (blocking)**: Guarantees it completes
before the login success event is sent
- **Subsequent events use `linked_principal_id`**: Once aliased, all
future events use the authenticated ID
- **Lazy aliasing**: If a user authenticates via another mechanism (not
through `arcade login`), the system detects this on the next command and
performs aliasing before sending that command's event
### **Event Capture Pipeline**
When `CommandTracker.track_command_execution()` is called:
1. **Resolve identity** → determines `distinct_id` and `is_anon` flag
2. **Build event properties**:
```python
{
"command_name": "toolkit.run",
"cli_version": "1.2.3",
"python_version": "3.11.0",
"os_type": "Darwin",
"os_release": "23.4.0",
"duration": 1250.42, # milliseconds
"error_message": "..." # if failed
}
```
3. **Call `UsageService.capture()`**:
- Serializes event data to JSON
- Spawns detached subprocess: `python -m arcade_cli.usage`
- Passes data via `ARCADE_USAGE_EVENT_DATA` env var
- **Returns immediately** (non-blocking)
4. **Detached subprocess (`__main__.py`)**:
- Runs independently, survives parent CLI exit
- Deserializes event data
- If `is_anon=True`, sets `$process_person_profile=False` (tells PostHog
not to create a full profile)
- Sends event to PostHog with 5s timeout
- Exits (hard exit after 10s max via timeout thread)
### **Concurrency Handling**
Multiple CLI processes can run simultaneously. The system handles this
via:
- **File locking** on `usage.json` (shared lock for reads, exclusive for
writes)
- **Atomic writes** via temp files ensure incomplete writes never
corrupt the file
- **Idempotent aliasing**: `should_alias()` prevents redundant alias
calls
### **Edge Cases Handled**
1. **Side-channel authentication**: User authenticates outside of
`arcade login` (e.g., manually editing credentials)
- Detected via "lazy aliasing" check on every command
- Performs alias if `linked_principal_id` doesn't match current
`principal_id`
2. **API failures during identity fetch**: Falls back to anonymous
tracking
- 2s timeout prevents hanging
- Silent failure doesn't disrupt CLI
3. **PostHog merge restrictions**: Can't alias returning users who
already have a profile
- System stores `linked_principal_id` to avoid retrying impossible
aliases
- New users (never logged in before) get full history stitched
4. **Multiple accounts on same machine**: Logout rotates `anon_id`
- User A's anonymous activity won't leak into User B's profile
### **Privacy & Performance**
- **Opt-out**: `ARCADE_USAGE_TRACKING=0` disables all tracking
- **Non-blocking**: Events never slow down CLI (detached subprocess)
- **Anonymous profiles**: `$process_person_profile=False` for `anon_id`
events minimizes data collection
- **Silent failures**: Network issues or PostHog errors never surface to
users
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