fix: UTF-8 safe string truncation in browser tool and debug logging

[l33t0]

Summary

Fixes remaining unsafe byte-level string slicing (&s[..N]) that panics when truncation lands inside a multi-byte UTF-8 character (Cyrillic, CJK, emoji).

• src/tools/browser.rs - 3 locations: DOM node name (200), input value (100), typed text display (50)
• src/main.rs - 2 locations: OAuth token debug logging (20)

All switched to floor_char_boundary(), matching the pattern already used across the rest of the codebase.

Note: the file_read tool mentioned in #391 is actually already safe - it uses line-based slicing and truncate_at_char_boundary(). The real culprits were these browser/debug paths.

Closes #391

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Also fixes a pre-existing clippy collapsible_if lint in src/tools/send_message_to_another_channel.rs that was failing CI on main after the Signal adapter merge.

Test plan

• cargo clippy --all-targets -- -D warnings passes clean
• cargo test --lib -- file — all 16 tests pass
• Manually test browser tool with CJK/Cyrillic content exceeding truncation limits

Note

This fix eliminates 5 unsafe byte-slicing vulnerabilities across two files by replacing direct slice operations with UTF-8 boundary-aware truncation. Changes are limited to debug output formatting in OAuth logging and DOM snapshot rendering for the browser tool.

_{Written by Tembo for commit c902563. This will update automatically on new commits.}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 3cf2dc92-4545-4ee0-a941-ecf4e06f5306

📥 Commits

Reviewing files that changed from the base of the PR and between 81c1bb8 and e3b6e31.

📒 Files selected for processing (2)

• src/main.rs
• src/tools.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/main.rs

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Walkthrough

This PR introduces UTF-8 safe truncation mechanisms across the codebase to prevent panics when processing multibyte character sequences. Changes include replacing manual byte-slicing with a character-boundary-aware helper function, adding comprehensive unit tests for edge cases, and updating token output formatting in authentication status commands.

Changes

Cohort / File(s)	Summary
Token Output Formatting src/main.rs	Updated cmd_auth status output to redact access and refresh tokens with a placeholder and display byte length instead of showing first 20 characters.
UTF-8 Safe Truncation Implementation src/tools/browser.rs	Replaced three manual byte-slicing truncations with truncate_utf8_ellipsis() helper for safe handling of node names, values, and typed text in browser snapshot rendering.
UTF-8 Truncation Test Suite src/tools.rs	Added six unit tests validating UTF-8 boundary handling for Cyrillic, CJK, emoji, mixed multibyte content, and truncate_output function across various byte limits and edge cases.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• PR #276: Implements UTF-8 safe character-boundary-aware truncation using similar helper functions to prevent multibyte-slice panics.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR includes a secondary fix for a clippy collapsible_if lint in src/tools/send_message_to_another_channel.rs that is not mentioned in the PR objectives or #391 requirements, representing an out-of-scope change.	Either remove the collapsible_if fix from this PR and create a separate PR for it, or update the PR description to explicitly document this secondary lint fix and its justification.
Docstring Coverage	⚠️ Warning	Docstring coverage is 70.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately summarizes the main change: fixing UTF-8 safe string truncation across the browser tool and debug logging components.
Description check	✅ Passed	The description is well-related to the changeset, providing context about UTF-8 vulnerabilities being fixed and locations affected (browser.rs and main.rs token logging).
Linked Issues check	✅ Passed	The PR successfully addresses the core objective from #391: replacing unsafe byte-level string slicing with UTF-8-aware truncation using floor_char_boundary() across five locations (3 in browser.rs, 2 in main.rs) and adds comprehensive unit tests for Cyrillic, CJK, and emoji content.

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