refactor: extract shared helpers for task ID validation, file resolution, and frontmatter writing

[lukstafi]

Summary

Follow-up to PR #79 — extracts duplicated logic from dashboard-server.ts into shared helpers to prevent a class of copy-paste bugs caught in the retrospective.

• TASK_ID_RE — exported from src/tasks/markdown.ts, replaces four inline regexes across dashboard-server.ts
• resolveTaskFile(taskId) — local helper inside startDashboardServer that centralises the resolve + safety-check + existence-check pattern used by task-promote, task-confirm, task-dismiss
• updateFrontmatterField / addFrontmatterField — existing helpers from tasks/markdown.ts now used in both /api/slot-postpone and /api/task-promote, replacing two hand-rolled 15-line frontmatter loops
• priorityValue() — exported from src/tasks/markdown.ts, imported into dashboard.ts; dead copy in flow.ts removed
• Unit tests — src/tasks/priority-value.test.ts tests S < A < B < C ordering and unknown → 9

Test plan

• bun run typecheck — clean
• bun test — 257 pass, 0 fail (includes 4 new priorityValue tests)

🤖 Generated with Claude Code

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: bde642194f

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Scope priority-field check to frontmatter before promote write

Calling addFrontmatterField(taskFile, "priority", newPriority) here can silently fail to persist a promotion when the task has no priority in frontmatter but the markdown body contains a top-level priority: line. addFrontmatterField checks existence with content.includes("\npriority:") (in src/tasks/markdown.ts) and may choose updateFrontmatterField, which only edits inside frontmatter and therefore performs no insertion; the API still returns the new priority, so UI/ordering can diverge from the file state.

Useful? React with 👍 / 👎.

[lukstafi]

Retrospective: What I'd Do Differently Next Time

task-010fa0f1 — Dashboard API cleanup: extract shared helpers

1. Verify call sites before deleting a "duplicate" function

Before removing priorityValue() from flow.ts, I should have confirmed it was genuinely dead
code (never called), not just checking for the definition. In this case it was dead, but the right
habit is: grep -n 'priorityValue(' src/flow.ts first, then decide. Removing a function that
turns out to be called somewhere would cause a typecheck failure that I'd need to recover from.

2. Audit utility functions for whole-file scans before delegating to them

addFrontmatterField had a latent bug: content.includes("\nfield:") scanned the whole file,
not just the frontmatter. Before replacing a hand-rolled loop with a utility call, I should read
the utility's implementation and check for assumptions like "the content is frontmatter-only".
Had I done this during the initial refactor, the reviewer catch (PR comment round) would not have
been needed — the fix would have been in the first commit.

Checklist for future utility delegation:

• Does the utility scope its search correctly (frontmatter-only vs whole file)?
• Does it handle the "key absent" case in the same way as the code being replaced?
• Are there edge cases (body contains the same key name) that differ from the original behaviour?

3. Add a regression test for the body-scope bug when fixing it

The addFrontmatterField body-scope fix was committed without a dedicated test that would have
caught the original bug and proves the fix. Next time, when addressing a reviewer comment about a
subtle edge case, add a test alongside the fix:

test("addFrontmatterField ignores body lines when checking existence", () => {
  // file has no frontmatter priority: field, but body contains "priority: foo"
  // addFrontmatterField should INSERT into frontmatter, not silently no-op
});

4. The proposal's flow.ts section was slightly misleading

The proposal said "Update flow.ts — remove local priorityValue(), import shared version". The
function was never called, so the right action was only the deletion, not adding an import. When
following a proposal, verify each step against actual call sites rather than treating the proposal
as ground truth.