fix(notifications): use safe UTF-8 slicing for session IDs

[echobt]

Summary

Fixes #5274 - Notification session ID slicing panics on multi-byte UTF-8.

Problem

Session ID string handling uses byte-based slicing which can panic on multi-byte UTF-8 characters when the slice boundary falls in the middle of a character.

Solution

Used safe string slicing with char boundaries - iterates through character indices to find the last valid UTF-8 boundary at or before position 8, then uses .get() for safe slicing.

[greptile-apps]

Greptile Overview

Greptile Summary

This PR replaces unsafe byte-based string slicing with UTF-8 character boundary aware slicing to prevent panics when slicing multi-byte UTF-8 characters.

Changes Made:

• import_cmd.rs: Replaced all direct byte slicing ([start..], [..end]) with safe .get() methods that return Option<&str>, gracefully handling invalid boundaries by continuing to the next iteration
• notification.rs: Replaced [..8.min(len)] with character-aware slicing logic using char_indices() to find valid UTF-8 boundaries

Issues Found:

• Logic bug in notification.rs:69 where the condition checks if character start index is <8 rather than checking if character end position is ≤8, allowing characters that straddle the 8-byte boundary to be included (e.g., a 4-byte emoji starting at byte 7 would extend the result to 11 bytes)

Confidence Score: 2/5

• This PR has a logic bug in notification.rs that violates the intended 8-byte truncation constraint
• The import_cmd.rs changes are correct and robust, but notification.rs contains a subtle logic error where multi-byte characters can cause the result to exceed the intended 8-byte limit
• src/cortex-cli/src/utils/notification.rs requires attention due to the boundary check logic error

Important Files Changed

Filename	Overview
src/cortex-cli/src/utils/notification.rs	Replaced unsafe byte slicing with UTF-8 aware slicing, but has logic bug that can exceed 8-byte limit when multi-byte chars straddle the boundary
src/cortex-cli/src/import_cmd.rs	Correctly replaced all unsafe byte slicing with safe .get() methods that gracefully handle invalid UTF-8 boundaries

Sequence Diagram

sequenceDiagram
    participant Caller
    participant send_task_notification
    participant String Slicing
    participant send_notification
    
    Caller->>send_task_notification: session_id, success
    send_task_notification->>String Slicing: Truncate session_id to ~8 bytes
    Note over String Slicing: char_indices().take_while(idx < 8)<br/>map to char end positions<br/>get last position
    String Slicing-->>send_task_notification: short_id
    send_task_notification->>send_notification: title, body, urgency
    send_notification-->>Caller: Result

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[greptile-apps]

_{2 files reviewed, 1 comment}

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[greptile-apps]

Logic bug: take_while(|(idx, _)| *idx < 8) takes chars whose start index is <8, but doesn't check if they exceed 8 bytes when included. If a 4-byte char starts at index 7, it extends to byte 11.

Suggested change

	.take_while(|(idx, _)| *idx < 8)
	.take_while(|(idx, ch)| idx + ch.len_utf8() <= 8)

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/cortex-cli/src/utils/notification.rs
Line: 69:69

Comment:
Logic bug: `take_while(|(idx, _)| *idx < 8)` takes chars whose start index is <8, but doesn't check if they exceed 8 bytes when included. If a 4-byte char starts at index 7, it extends to byte 11.

```suggestion
        .take_while(|(idx, ch)| idx + ch.len_utf8() <= 8)
```

How can I resolve this? If you propose a fix, please make it concise.

[echobt]

Consolidated into #70 - fix: consolidated UTF-8 safety improvements for string slicing