fix(mantis): publish proof comments on auto-triggered runs (#127787)

## What Problem This Solves

Auto-triggered Mantis proof runs (label/`clawsweeper_label` and other non-comment request sources) end with no PR comment at all. The durable evidence publisher runs with `--create-missing false` and only edits an existing marker comment, but the inline status comment carrying that marker was only created when `request_source == 'issue_comment'`. Label-triggered runs therefore published nothing and logged the misleading "Skipped stale Mantis QA evidence comment because its status is no longer active" — observed on PR #127735. This is the silent-failure class: a Mantis run completes and the PR shows no visible outcome.

## Why This Change Was Made

- `.github/workflows/mantis-telegram-desktop-proof.yml`: the status ack comment (👀 + active-job link + run-scoped marker) is now created for every request source that resolves to a PR (`pr_number != ''`), not only `issue_comment`. The 👀 *reaction* stays `issue_comment`-only (it lives in `mantis-resolve-request.yml`, untouched — there is no triggering comment to react to on label runs).
- The start-failure fallback comment and the existing-artifact republish path now use the same run-scoped marker `<!-- mantis-telegram-desktop-proof:${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT} -->` as the status comment and the main publisher, so every publisher edits the single run-owned comment (ack → progress → final proof; no comment spam). The republish path gets an explicit `--create-missing false` to match. The design invariant that makes `false` safe: the fallback status-comment step is not `continue-on-error`, so a run in which no marker comment could be created fails `resolve_request` and never reaches publish.
- `scripts/mantis/publish-pr-evidence.mjs`: the two skip cases now log honestly — "no existing comment found" vs "could not update existing comment" — instead of one misleading stale-status message.

## User Impact

Operators triggering Mantis via labels (ClawSweeper flows) now get the same single evolving PR comment as comment-triggered runs: an immediate 👀 ack with the running job link, edited in place into the final proof evidence. No more runs that finish invisibly.

## Evidence

- Focused suite: `node scripts/run-vitest.mjs test/scripts/mantis-telegram-desktop-proof-workflow.test.ts` — 28/28, including new assertions that the status/failure comment gates use `pr_number != ''` (and not `request_source`) and that both publishers pass the run-scoped marker with `--create-missing false`.
- `node scripts/check-changed.mjs -- <touched files>` green; `git diff --check` clean.
- Marker alignment verified across all five sites in the workflow (status comment, prior-attempt cleanup regex, fallback comment, failure report, both publisher invocations): all use `mantis-telegram-desktop-proof:${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}`.
- Live-run proof of the label-triggered path requires a merged workflow (GitHub runs the workflow from the default branch for these triggers), so the first post-merge label-triggered Mantis run is the live verification; stated here as the known evidence gap.

Production LOC delta: −4 (workflow/tooling); tests +13.

test/scripts/mantis-telegram-desktop-proof-workflow.test.ts

@@ -382,10 +382,11 @@ describe("Mantis Telegram Desktop proof workflow", () => {
     const fallbackComment = resolver?.steps?.find(
       (step) => step.name === "Report Mantis start failure with workflow token",
     );
-    expect(startedToken?.if).toContain("request_source == 'issue_comment'");
+    expect(startedToken?.if).toBe("${{ steps.resolve.outputs.pr_number != '' }}");
+    expect(startedToken?.if).not.toContain("request_source");
     expect(startedToken?.with?.["permission-pull-requests"]).toBe("write");
     expect(startedComment?.["continue-on-error"]).toBe(true);
-    expect(startedComment?.with?.script).toContain("Mantis started this proof.");
+    expect(startedComment?.with?.script).toContain("👀 Mantis started this proof.");
     expect(startedComment?.with?.script).toContain("actions/runs/${process.env.GITHUB_RUN_ID}");
     expect(startedComment?.with?.script).toContain("mantis-telegram-desktop-proof:");
     expect(startedComment?.with?.script).toContain("GITHUB_RUN_ATTEMPT");
@@ -393,6 +394,8 @@ describe("Mantis Telegram Desktop proof workflow", () => {
     expect(startedComment?.with?.script).toContain("issues.deleteComment");
     expect(fallbackComment?.if).toContain("steps.mantis_status_token.outcome != 'success'");
     expect(fallbackComment?.if).toContain("steps.mantis_status_comment.outcome != 'success'");
+    expect(fallbackComment?.if).toContain("steps.resolve.outputs.pr_number != ''");
+    expect(fallbackComment?.if).not.toContain("request_source");
     expect(fallbackComment?.with?.["github-token"]).toBe("${{ github.token }}");
     expect(fallbackComment?.["continue-on-error"]).toBeUndefined();
     expect(fallbackComment?.with?.script).toContain("mantis-telegram-desktop-proof");
@@ -406,7 +409,8 @@ describe("Mantis Telegram Desktop proof workflow", () => {
     const failureComment = proofSteps.find((step) => step.name === "Report failed Mantis proof");
     expect(evidenceComment?.id).toBe("publish_evidence");
     expect(failureComment?.if).toContain("always()");
-    expect(failureComment?.if).toContain("request_source == 'issue_comment'");
+    expect(failureComment?.if).toContain("needs.resolve_request.outputs.pr_number != ''");
+    expect(failureComment?.if).not.toContain("request_source");
     expect(failureComment?.if).toContain("steps.publish_evidence.outcome != 'success'");
     expect(failureComment?.with?.script).toContain("Mantis could not complete this proof.");
     expect(failureComment?.with?.script).toContain("issues.updateComment");
@@ -454,6 +458,15 @@ describe("Mantis Telegram Desktop proof workflow", () => {
     expect(workflowText).toContain(
       "PUBLISH_ARTIFACT_URL=https://github.com/${GITHUB_REPOSITORY}/actions/runs/",
     );
+    const evidenceComment = jobStep(
+      WORKFLOW,
+      "publish_existing_telegram_desktop_proof",
+      "Comment PR with inline QA evidence",
+    );
+    expect(evidenceComment.run).toContain(
+      "mantis-telegram-desktop-proof:${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}",
+    );
+    expect(evidenceComment.run).toContain("--create-missing false");
   });
 
   it("limits evidence publishers to comment and PR-read permissions", () => {