fix(clippy): use sort_by_key with Reverse for descending sorts

[mateodelnorte]

Summary

Rust 1.95.0 added the unnecessary_sort_by lint, which fires on sort_by(|a, b| b.cmp(&a)) patterns since they're equivalent to sort_by_key(|x| std::cmp::Reverse(x)). Three call sites were caught when meta's CI re-ran for the first time in two weeks against this repo's cloned main.

Changes (mechanical, matches clippy's suggested fix exactly):

• src/agent_guard.rs:275 — pattern compile-time sort by priority
• src/agent_score.rs:119 — session list sort by mtime
• src/dependency_graph.rs:410 — dependent count sort

No functional change — sort order is preserved.

Why this matters now

gitkb/meta#78 (adding Discord release notification) is blocked on clippy. Meta's CI clones this repo's main fresh, so this needs to land first to unblock the meta PR.

Test plan

• CI clippy passes (verifies the lint fix locally — full workspace clippy needs sibling repos which weren't in scope)

Summary by CodeRabbit

• Refactor
  • Enhanced internal code quality through optimized sorting implementations across pattern compilation, session management, and dependency analysis systems. All existing functionality is preserved with no impact to user-facing features.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 112b1288-0a27-4ee0-8295-856f6fc095ea

📥 Commits

Reviewing files that changed from the base of the PR and between 1286eda and ce3a5dc.

📒 Files selected for processing (3)

• src/agent_guard.rs
• src/agent_score.rs
• src/dependency_graph.rs

---

Walkthrough

Three sorting implementations across distinct modules were refactored from sort_by with manual comparators to sort_by_key with std::cmp::Reverse, maintaining descending order semantics. No behavioral changes occurred.

Changes

Cohort / File(s)	Summary
Sorting refactoring src/agent_guard.rs, src/agent_score.rs, src/dependency_graph.rs	Simplified descending-order sort implementations by replacing sort_by with manual comparators (b.cmp(&a)) with sort_by_key using std::cmp::Reverse. Affects pattern priority ordering, session transcript modification times, and dependency counts respectively.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

Sorts that once were long and grand,
Now with Reverse take their stand—
Three brief lines of rabbit cheer,
Cleaner code, more crystal clear! 🐰✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and specifically describes the main change: replacing sort_by comparators with sort_by_key using Reverse for descending sorts across three files.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch meta-cli-clippy

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