#234: Fix code review findings — 5 HIGH, 8 MEDIUM, 6 LOW severity

[JeremyDev87]

Summary

Addresses all actionable findings from the 2026-02-12 comprehensive code review (issue #234). Supersedes closed draft PR #239.

HIGH severity (5)

• H1: Remove untrusted plan comment fallback in findPlanComment() — only trusted bot authors accepted
• H2: Escape labels/author in execute prompt shell templates via escapeArrayForShellArg()
• H3: Reject NONE in authorized_approvers validation
• H4: Replace unsafe as LeonidasMode cast with isValidLeonidasMode() type guard
• H5: Replace unsafe as Command cast with isValidCommand() type guard

MEDIUM severity (8)

• M1: Register API key and GitHub token with core.setSecret() in main.ts
• M2: Add newline/carriage-return escaping to escapeForShellArg()
• M5: Cache Octokit instances by token (Map-based singleton)
• M6: Use path.join() instead of string interpolation for file paths
• M12: Add coverage/** to ESLint ignores
• E1: Validate MODE env var in post_process_cli.ts (remaining as LeonidasMode)
• E2: Register GH_TOKEN with core.setSecret() in all post_process_cli.ts functions
• E3: Escape single-quotes and strip control characters in escapeForShellArg()

LOW severity (6)

• L1: Extract magic number 5 to named constant RESERVED_TURNS
• L4: Strict parseRepo() validation — reject empty, missing separator, and extra path segments
• L5: Restrict temp prompt file permissions to 0o600
• E4: Reject extra path segments in parseRepo() (e.g., owner/repo/extra)
• E5: Remove unnecessary as Command in isValidCommand()
• E6: Add cross-platform comment for mode: 0o600

Skipped (false positives / already resolved)

• M3: allowed_tools default — documented design decision
• M4: Plan comment wrapping — already uses wrapUserContent()
• M7: i18n test coverage — all 8 languages confirmed tested
• M10: run() refactoring — already done
• L3: Silent catch in linkSubIssues — already fixed

Closes #234

Test plan

• All 427 tests pass (npx vitest run)
• npm run lint passes (ESLint + Prettier)
• npm run typecheck passes (tsc --noEmit)
• npm run build succeeds (ncc bundle)
• Code review: APPROVE (0 Critical, 0 High, 0 Medium remaining)
• Security review: APPROVE (all injection vectors mitigated)