feat(engine): implement systematic debugging mode

[robertotru]

What

Implemented the systematic debugging mode within canon-engine to enable a recommendation-only, green-zone workflow for codebase troubleshooting, incident isolation, and validation.

Why

This change is needed to address roadmap feature 01-systematic-debugging, establishing a structured five-step gate system to ensure incidents undergo rigorous verification and post-incident root-cause analysis before closure.

How

• Registered the new debugging mode in the domain model and classifier.
• Defined and implemented the debugging mode gatekeeper logic in crates/canon-engine/src/modes/debugging.rs.
• Enforced a 5-phase artifact verification contract:
  • 01-context (Incident background and initial assumptions)
  • 02-reproduction (Test harness, script, or environment setups)
  • 03-root-cause (Diagnostic isolation and analysis evidence)
  • 04-fix-decision (Remediation choices and tradeoffs)
  • 05-verification (Evidence demonstrating red-to-green state transition)
• Bumps workspace crates and compatibility manifests to 0.65.0.
• Removed the completed feature document from roadmap/features/ and updated modes guides (tech-docs/guides/modes.md and docs/guide/canon-modes.md).

Validation

• Added a full integration test suite in tests/debugging_run.rs verifying gate checks, missing artifact blocks, and transition paths.
• Ran cargo test and cargo nextest run to ensure all existing and new tests pass cleanly.
• Validated workspace constraints with cargo clippy --workspace --all-targets --all-features -- -D warnings and cargo fmt.

Checklist

• The change is scoped to one real problem and avoids unrelated cleanup.
• I updated docs, specs, or release-facing surfaces when behavior changed.
• I ran the relevant validation for the surfaces I touched.
• If I touched install, packaging, or release behavior, I kept those surfaces aligned.
• If I touched skills or assistant package surfaces, I validated those paths too.

[codecov]

Codecov Report

❌ Patch coverage is 99.73545% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...non-engine/src/orchestrator/service/mode_change.rs	98.18%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud