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therefore published nothing and logged the misleading "Skipped stale Mantis QA evidence comment because its status is no longer active" — observed on PR #127735.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.

.github/workflows/mantis-telegram-desktop-proof.yml

@@ -181,7 +181,7 @@ jobs:
             setOutput("request_source", requestSource);
       - name: Create Mantis status token
         id: mantis_status_token
-        if: ${{ steps.resolve.outputs.request_source == 'issue_comment' }}
+        if: ${{ steps.resolve.outputs.pr_number != '' }}
         continue-on-error: true
         uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1 # v3
         with:
@@ -201,12 +201,9 @@ jobs:
         with:
           github-token: ${{ steps.mantis_status_token.outputs.token }}
           script: |
-            const markerRoot = "<!-- mantis-telegram-desktop-proof:";
-            const runId = Number(process.env.GITHUB_RUN_ID);
-            const runAttempt = Number(process.env.GITHUB_RUN_ATTEMPT);
-            const marker = `${markerRoot}${runId}-${runAttempt} -->`;
+            const marker = `<!-- mantis-telegram-desktop-proof:${process.env.GITHUB_RUN_ID}-${process.env.GITHUB_RUN_ATTEMPT} -->`;
             const runUrl = `${process.env.GITHUB_SERVER_URL}/${process.env.GITHUB_REPOSITORY}/actions/runs/${process.env.GITHUB_RUN_ID}`;
-            const body = `${marker}\nMantis started this proof. [Follow the active job](${runUrl}).`;
+            const body = `${marker}\n👀 Mantis started this proof. [Follow the active job](${runUrl}).`;
             const { owner, repo } = context.repo;
             const issueNumber = Number(process.env.TARGET_PR);
             await github.rest.issues.createComment({
@@ -248,7 +245,7 @@ jobs:
         if: >-
           ${{
             always() &&
-            steps.resolve.outputs.request_source == 'issue_comment' &&
+            steps.resolve.outputs.pr_number != '' &&
             (
               steps.mantis_status_token.outcome != 'success' ||
               steps.mantis_status_comment.outcome != 'success'
@@ -260,7 +257,7 @@ jobs:
         with:
           github-token: ${{ github.token }}
           script: |
-            const marker = "<!-- mantis-telegram-desktop-proof -->";
+            const marker = `<!-- mantis-telegram-desktop-proof:${process.env.GITHUB_RUN_ID}-${process.env.GITHUB_RUN_ATTEMPT} -->`;
             const runUrl = `${process.env.GITHUB_SERVER_URL}/${process.env.GITHUB_REPOSITORY}/actions/runs/${process.env.GITHUB_RUN_ID}`;
             const { owner, repo } = context.repo;
             await github.rest.issues.createComment({
@@ -1238,7 +1235,7 @@ jobs:
             --request-source "$REQUEST_SOURCE"
 
       - name: Report failed Mantis proof
-        if: ${{ always() && needs.resolve_request.outputs.request_source == 'issue_comment' && steps.publish_evidence.outcome != 'success' }}
+        if: ${{ always() && needs.resolve_request.outputs.pr_number != '' && steps.publish_evidence.outcome != 'success' }}
         uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
         env:
           TARGET_PR: ${{ needs.resolve_request.outputs.pr_number }}
@@ -1367,7 +1364,8 @@ jobs:
             --manifest "$root/mantis-evidence.json" \
             --target-pr "$TARGET_PR" \
             --artifact-root "mantis/telegram-desktop/pr-${TARGET_PR}/published-${PUBLISH_RUN_ID}-${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}" \
-            --marker "<!-- mantis-telegram-desktop-proof -->" \
+            --marker "<!-- mantis-telegram-desktop-proof:${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT} -->" \
+            --create-missing false \
             --artifact-url "$PUBLISH_ARTIFACT_URL" \
             --run-url "https://github.com/${GITHUB_REPOSITORY}/actions/runs/${PUBLISH_RUN_ID}" \
             --request-source "$REQUEST_SOURCE"