> ## Documentation Index
> Fetch the complete documentation index at: https://dev-doc.dualmindlab.tech/llms.txt
> Use this file to discover all available pages before exploring further.

# PATCH /api/threads/{id}

> Update thread title

## Authentication

**Required**: JWT Bearer token

**JWT Claims Extraction** (Lines 277-281):

```csharp theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
sub | ClaimTypes.NameIdentifier → User UUID (required)
```

## Path Parameters

<ParamField path="id" type="string" required>
  Thread UUID

  **Format**: Valid GUID

  **Validation**: Route constraint `:guid` (Line 270)
</ParamField>

## Request Body

<ParamField body="title" type="string" required>
  New thread title

  **Validation** (Lines 305-313):

  ```csharp theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  if (string.IsNullOrWhiteSpace(request?.Title)) {
      return BadRequest("Title is required");
  }
  ```

  **Constraints**:

  * MUST NOT be null
  * MUST NOT be empty string
  * MUST NOT be whitespace-only

  **Max Length**: Not enforced by API contract (database column limit may apply)
</ParamField>

<RequestExample>
  ```bash cURL theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  curl -X PATCH 'http://localhost:5079/api/threads/f47ac10b-58cc-4372-a567-0e02b2c3d479' \
    -H 'Authorization: Bearer YOUR_JWT_TOKEN' \
    -H 'Content-Type: application/json' \
    -d '{"title": "Updated Thread Title"}'
  ```

  ```javascript JavaScript theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  const response = await fetch(
    'http://localhost:5079/api/threads/f47ac10b-58cc-4372-a567-0e02b2c3d479',
    {
      method: 'PATCH',
      headers: {
        'Authorization': `Bearer ${jwt}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        title: 'Updated Thread Title'
      })
    }
  );

  const result = await response.json();
  ```

  ```python Python theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  import requests

  response = requests.patch(
      'http://localhost:5079/api/threads/f47ac10b-58cc-4372-a567-0e02b2c3d479',
      headers={
          'Authorization': f'Bearer {jwt}',
          'Content-Type': 'application/json'
      },
      json={'title': 'Updated Thread Title'}
  )

  result = response.json()
  ```
</RequestExample>

<ResponseExample>
  ```json 200 Success theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "success": true,
    "message": "Thread updated successfully"
  }
  ```

  ```json 400 INVALID_REQUEST theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "success": false,
    "error": "Title is required",
    "code": "INVALID_REQUEST"
  }
  ```

  ```json 401 Unauthorized theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "error": "User ID claim missing"
  }
  ```

  ```json 404 NOT_FOUND theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "success": false,
    "error": "Thread not found",
    "code": "NOT_FOUND"
  }
  ```

  ```json 403 FORBIDDEN theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "success": false,
    "error": "You do not have permission to update this thread",
    "code": "FORBIDDEN"
  }
  ```

  ```json 500 THREAD_UPDATE_ERROR theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
  {
    "success": false,
    "error": "Database update failed",
    "code": "THREAD_UPDATE_ERROR"
  }
  ```
</ResponseExample>

## Authorization

**Ownership Verification** (Lines 289-303):

```csharp theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
var thread = await _threadsService.GetThreadAsync(threadId);
if (thread == null) {
    return NotFound("Thread not found");
}

if (thread.UserId != userId) {
    return 403 FORBIDDEN;
}
```

**Permission Rules**:

* ONLY thread owner can update title
* No delegation or sharing of update rights
* Admins NOT exempted (no admin check in code)

## Side Effects

**Database Mutations** (Line 315):

```csharp theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
await _threadsService.UpdateThreadAsync(threadId, request.Title);
```

**Tables Written**:

* UPDATE `threads` SET `title = {request.Title}`, `updated_at = NOW()` WHERE `thread_id = {threadId}`

**Cascade Effects**: None

* Messages not affected
* Thread visibility not changed
* Ownership not changed

## Permissions

**Who Can Modify**:

* Thread owner only

**Who Cannot Modify**:

* Other authenticated users
* Unauthenticated users
* Public thread viewers (even if public\_sharing enabled)

## Edge Cases

1. **Thread doesn't exist**: 404 (Lines 290-293)
2. **User is not owner**: 403 (Lines 295-303)
3. **Title is null**: 400 (Lines 305-313)
4. **Title is empty**: 400 (Lines 305-313)
5. **Title is whitespace-only**: 400 (Lines 305-313)
6. **Title same as current**: Update proceeds (no change detection)
7. **Very long title**: Not validated by controller (database may truncate or error)

## Error Conditions

| Code                  | HTTP | Cause                       | Controller Line |
| --------------------- | ---- | --------------------------- | --------------- |
| N/A                   | 401  | JWT missing or invalid      | Middleware      |
| N/A                   | 401  | User ID claim missing       | 283-286         |
| `INVALID_REQUEST`     | 400  | Title null/empty/whitespace | 305-313         |
| `NOT_FOUND`           | 404  | Thread doesn't exist        | 290-293         |
| `FORBIDDEN`           | 403  | Not thread owner            | 295-303         |
| `THREAD_UPDATE_ERROR` | 500  | Service exception           | 323-331         |

**Exception Handling** (Lines 323-331):

```csharp theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
catch (Exception ex) {
    return StatusCode(500, new { error = ex.Message, code = "THREAD_UPDATE_ERROR" });
}
```

## Behavioral Guarantees

**Atomicity**: Single UPDATE query (atomic)

**Idempotency**: NOT idempotent

* `updated_at` timestamp changes on every call
* Even if title unchanged

**Concurrency**: No locking

* Race condition possible if two updates concurrent
* Last write wins (database-dependent)

## Validation Order

1. User ID from JWT (401 if missing)
2. Thread existence (404 if not found)
3. Ownership (403 if not owner)
4. Title validation (400 if invalid)
5. Update execution (500 if fails)

**Note**: Title validated AFTER ownership check (Lines 305-315)

## Database Schema Impact

**Column Updated**: `threads.title`

**Timestamp Updated**: `threads.updated_at` (implicit, service-level)

**No Triggers**: Controller doesn't document any database triggers