feat: add Swift/PHP/Kotlin/Shell post-edit diagnostics

[Ayush7614]

Summary

• Extends post-edit diagnostics with PATH-gated linters for Swift (swiftlint), PHP (phpstan → pint → php -l), Kotlin (ktlint), and Shell (shellcheck).
• Tools are never auto-installed; missing binaries are silently skipped (same pattern as Ruby/rubocop).
• Adds unit coverage and updates the README diagnostics list.

Closes #2

Test plan

• bun run typecheck
• bun test (190 pass)
• bun run bench:selfcheck
• bun run build
• Spot-check with a tool on PATH (e.g. shellcheck) editing a .sh file in the TUI

[github-actions]

🤖 KlaatAI Review Bot (powered by Klaatu, advisory only — a maintainer makes the real call)

Issue match
No linked issue (null). Reviewers must manually confirm the PR's scope matches the intended feature request.

Test coverage
Tests were added in src/tools/diagnostics.test.ts. They cover negative paths: ensuring no exceptions when binaries are absent, returning null when disabled, and verifying explicit config overrides win. Missing is positive-path coverage (e.g., mocking onPath to return true) to verify the correct CLI arguments are actually constructed for the spawned processes.

Correctness concerns
In src/tools/diagnostics.ts, the PHP fallback chain (phpstan → pint → php -l) mixes semantic levels. phpstan and pint check style/static analysis, while php -l only checks syntax. If a user has php but not the others, they silently get a much weaker diagnostic. Additionally, verify ktlint --reporter=plain compatibility, as ktlint 1.0.0+ changed reporter flags.

Verdict
Needs human judgment call on whether the PHP php -l fallback is acceptable and if ktlint CLI flags need version-gating.

_{This is an automated review to help triage faster, not a gate. Nothing here blocks merging.}

[aakashrajput]

@Ayush7614 please link the issue to your PR, Thanks

[Ayush7614]

Linked to #2 (shellcheck / shell script diagnostics). This PR also adds the same PATH-gated pattern for Swift (swiftlint), PHP (phpstan/pint/php -l), and Kotlin (ktlint) alongside shellcheck.

[github-actions]

🤖 KlaatAI Review Bot (powered by Klaatu, advisory only — a maintainer makes the real call)

Issue match
The PR fully implements the shell script diagnostics requested in #2, but significantly expands scope by also adding Swift, PHP, and Kotlin. Issue #2 was strictly scoped to shell scripts.

Test coverage
Tests in src/tools/diagnostics.test.ts cover the "tool absent" and "diagnostics disabled" paths for all new extensions, plus config overrides. However, they lack coverage for the "tool present" execution path. A test mocking onPath to return true is needed to verify actual command construction and output parsing for these new linters.

Correctness concerns
In src/tools/diagnostics.ts, the shell branch includes .zsh. shellcheck explicitly does not support zsh and will emit false-positive errors for valid zsh syntax; .zsh should be removed from this block. Additionally, the PHP fallback to pint may yield confusing results on non-Laravel projects if the binary is globally installed.

Verdict
Needs human judgment call on scope creep (PR adds three languages beyond Issue #2's shell-only request) and a specific fix to remove .zsh from the shellcheck branch.

_{This is an automated review to help triage faster, not a gate. Nothing here blocks merging.}

[Ayush7614]

Addressed the review-bot notes in a follow-up commit:

• Removed .zsh from the shellcheck branch (shellcheck doesn’t support zsh)
• Dropped the php -l fallback (kept phpstan → pint only)
• Simplified ktlint argv (no --reporter flag for 1.x compatibility)
• Added positive-path tests via injectable PATH stubs on resolveDiagnosticsCommand

[github-actions]

🤖 KlaatAI Review Bot (powered by Klaatu, advisory only — a maintainer makes the real call)

Issue match
Partial. The PR fully implements the Shell diagnostics requested in issue #2, but significantly scope-creeps by also adding Swift, PHP, and Kotlin support, which were not requested in the linked issue.

Test coverage
Strong coverage in src/tools/diagnostics.test.ts. Tests verify soft-skips when tools are absent, disabled states, exact argv shapes via injected onPath stubs, config overrides, and explicitly assert .zsh is ignored. Missing: the PR's manual test plan checkbox for spot-checking a real tool on PATH remains unchecked, though CI coverage of the resolution logic is thorough.

Correctness concerns
Minor discrepancy: the PR body claims a php -l fallback for PHP, but src/tools/diagnostics.ts explicitly omits it. The code's choice is likely correct, but the PR description should be updated to match. Additionally, verify that ktlint's default plain output (without --reporter) doesn't cause parsing issues in the downstream runDiagnostics executor, given ktlint 1.x CLI changes.

Verdict
Needs human judgment call on whether to accept the scope creep (Swift/PHP/Kotlin) beyond issue #2's Shell-only request, and to confirm ktlint output parsing compatibility.

_{This is an automated review to help triage faster, not a gate. Nothing here blocks merging.}