Layer 4.2: Registry cleanup, docs, and full validation (FEAT-008)

[aboimpinto]

Refs #2870.
Follows #3652.

Summary

Layer 4.2 / FEAT-008 completes the registry cleanup, source-verified command architecture docs, and final validation evidence for the staged command-boundary work.

This branch was replayed onto current upstream main so the PR contains only the FEAT-008 surface after the already-merged Layer 4.1 work from #3652.

What changed

• Added registry guard coverage for duplicate built-in command names and aliases.
• Added an ownership-contract test for the final 9 group-owned command areas.
• Added a Gherkin eval smoke test proving the TUI binary loads and the eval harness reports step-level shell execution success.
• Updated docs/architecture/command-dispatch.md with the finalized command dispatch flow, command group boundaries, and permanent exceptions.
• Updated docs/architecture/pr-issue-evidence-prep.md with Layer 4.2 closure evidence and validation notes.

Gherkin E2E examples

New in this PR:

Feature: Eval smoke test (binary load and eval step reporting)

  Scenario: Binary loads and reports step-level success via eval
    Given a clean CodeWhale evaluation workspace
    When the evaluation harness runs a shell command
    Then the binary exits without crashing
    And the JSON report contains execution steps

Layer 4.x evidence also includes the previously-added plugin E2E coverage from #3652:

Feature: Plugin discovery and listing

  Scenario: Plugin scripts are discovered from the configured plugin directory
    Given an offline CodeWhale workspace with a configured plugin directory
    And the plugin directory contains:
      | name       | description                | approval |
      | greet      | Say hello to the user      | auto     |
      | audit      | Run a security audit       | required |
      | summarizer | Summarize the given input  | suggest  |
    When the plugin scanner discovers plugins
    Then the scanner should report 3 plugins

Validation

• cargo fmt --all -- --check
• cargo check -p codewhale-tui
• cargo test -p codewhale-tui command_registry_has_unique_names_and_aliases
• cargo test -p codewhale-tui command_ownership_contract_is_enforced
• cargo test -p codewhale-tui --test eval_smoke_acceptance
• git diff --check origin/main...HEAD

Paulo Aboim Pinto

[Hmbown]

Thank you @aboimpinto — this is a really strong validation/documentation slice. I rechecked the live state and the branch is clean against main, all required checks are green, and the scope is nicely focused on the Layer 4.2 registry cleanup/evidence surface.

I am holding off on merging only because the PR is still marked draft. Once you mark it ready for review, this looks like a good candidate for the 0.8.66+ lane, with the usual final maintainer read-through of the docs wording and validation claims before merge.

[aboimpinto]

I was waiting to check for conflicts. It's all ready now.

[Hmbown]

Merged into main as 5e9f7662ff7f9ec4766e35636634974a6e5e7544. Thank you again @aboimpinto — this was a careful, well-scoped validation/docs layer, and I really appreciate you checking conflicts and carrying it through to ready state so cleanly.