chore: remove dead code left by the v1.0 single-entrypoint refactor

[GautamSharma99]

Fixes #1668 (items 1–3). 167 deletions, no insertions.

Three independent commits, ordered least to most contentious, so any of them can be dropped without touching the others:

Commit	Removes
49b1663	checkTriggerAction + the now-unused @actions/core import
d90aa6c	updateTrackingComment (comments/update-with-branch.ts)
39aaabf	src/entrypoints/prepare.ts

Item 4 from the issue — the dead ALLOWED_TOOLS / DISALLOWED_TOOLS exports in create-prompt/index.ts — is not touched. Its trailing comment says it is kept so an H1 report's pointed-to file stays in sync with the live fix, and only maintainers can judge whether that still holds.

On the question I raised in #1668

I asked whether prepare.ts was retained deliberately before sending a deletion. Since I couldn't get an answer first, I went looking for evidence rather than assuming. It points to "left behind", and I'd rather show the work than ask you to take my word:

It has already drifted from the code that runs. The v1.0 refactor (#898) both moved the action to a single run.ts entrypoint and introduced WorkflowValidationSkipError handling. run.ts got it; prepare.ts never did:

Behaviour	run.ts	prepare.ts
WorkflowValidationSkipError handling	yes	no
skipped_due_to_workflow_validation_mismatch output	yes	no
Propagates GITHUB_TOKEN / GH_TOKEN to env	yes	no

So it isn't a redundant-but-equivalent copy; it is a stale description of the prepare phase. Anyone reading it to understand that phase gets the wrong answer.

Keeping it costs real maintenance. #1590 (acb0385, 4 Aug 2026) applied the workflow_run collaborator-permission change to prepare.ts and run.ts in parallel — a maintainer paid for the same change twice, and only one copy could ever execute. That is precisely the hazard this removes.

If it is being kept on purpose — a downstream consumer, or a documented manual invocation I couldn't find — drop commit 39aaabf and the other two still stand on their own.

Verification

$ grep -rn "entrypoints/prepare\|updateTrackingComment\|checkTriggerAction\|update-with-branch\|contains_trigger" \
    --exclude-dir=node_modules --exclude-dir=.git .
(no output)

Nothing anywhere in the repo — source, tests, workflows, docs, action.yml — still refers to any removed symbol or file. contains_trigger is included above because it was the only output checkTriggerAction produced, and it is not declared in action.yml.

• bun test — 920 pass, 0 fail
• bun run typecheck — clean
• bun run format:check — clean

One thing I deliberately left

Deleting update-with-branch.ts leaves createBranchLink in comments/common.ts with no production caller, though test/comments-common.test.ts still covers it. Its siblings createJobRunLink and createCommentBody are still used by create-initial.ts.

I left it rather than expanding scope: removing it means deleting test cases too, and it's a generic link-formatting helper that a maintainer may want to keep alongside its siblings. Happy to remove it and the corresponding tests if you'd prefer — say the word and it's a one-line follow-up.