Feature Request: Warn users before deleting a Google Drive file linked to a Claude project

### Problem Statement

**Feature Request: Warn users before deleting a Google Drive file linked to a Claude project**

**Summary**
When a Google Doc is added to a Claude project's knowledge base and subsequently deleted from Google Drive, Claude silently loses access to that file with no warning issued — either in Google Drive at the point of deletion, or in Claude after the fact. This is a data-loss risk that should be addressed.

**Current behavior**
- User links a Google Doc to a Claude project via the Drive connector
- User deletes the file from Google Drive
- Google Drive shows no warning that the file is linked to an external application
- Claude silently drops the file from project context with no notification to the user
- User only discovers the loss when Claude can no longer reference that material

**Expected behavior**
One or both of the following should occur:
1. **At deletion in Google Drive:** A warning surfaces stating the file is connected to a Claude project — similar to how Google Workspace warns when a shared file is about to be removed
2. **In Claude after deletion:** An active notification in the project knowledge panel flagging that a previously linked file is no longer accessible, with a prompt to re-link or replace it

**Why this matters**
The Claude Drive connector is read-only by design — it cannot write back to Drive or register a dependency flag on the file. This architectural decision is reasonable for security, but it creates a silent failure mode where users lose project context without any indication. For users relying on Drive-linked documents as core project knowledge (course materials, strategy docs, reference files), this is a meaningful data-loss risk with no safety net.

**Proposed fix**
- When a file is linked to a Claude project, Claude should register a lightweight metadata tag or comment on the file (requires minimal write permission — not full edit access)
- Google Drive should surface third-party dependency warnings before deletion, as it already does for shared files
- At minimum, Claude should poll linked files and proactively alert users inside the project when a linked file becomes inaccessible — before the user discovers it mid-conversation

**Related issue**
This is an extension of the gap documented in #497 (missing write/modify operations on the Drive connector). A deletion warning requires either a minimal write-back capability or a proactive sync-status check — both of which fall within the scope of that issue.

**Impact**
Any user who organizes or cleans up their Google Drive risks silently breaking their Claude project context. No current workaround exists other than manual tracking of which files are linked.

### Proposed Solution

Paste this exactly into that field:

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When a file is linked to a Claude project, one or more of the following should be implemented:

1. **Minimal write-back on link:** When a user adds a Google Doc to a Claude project, Claude registers a lightweight metadata tag on that file in Drive — just enough to signal "this file is in active use." This requires minimal write permission, not full edit access.

2. **Google Drive deletion warning:** Before a file is deleted in Google Drive, a warning surfaces if that file is tagged as linked to an external application — similar to how Google Workspace already warns before removing a shared file.

3. **Proactive sync-status check in Claude:** Claude periodically polls linked files in project knowledge. If a file becomes inaccessible — deleted, moved to restricted folder, or permissions changed — Claude immediately flags it inside the project panel with a clear alert and a prompt to re-link or replace it. The user finds out inside Claude, not mid-conversation when the context is already gone.

**Minimum acceptable fix:** Option 3 alone — no Drive-side changes required, fully within Anthropic's control, and eliminates the silent failure mode entirely.

### Alternatives Considered

_No response_

### Area

Resource Handling

### Priority

High - Major improvement needed

### Additional Context

_No response_