docs(merge-queue): remove /trunk stack from stacked-pull-requests page

[mintlify]

Summary

Removes the /trunk stack (combined-PR stacking via Trunk Sudo) documentation from merge-queue/using-the-queue/stacked-pull-requests.mdx. The page is rewritten to cover only the /trunk merge sequential-enqueue flow, which is unaffected and remains the supported way to merge a stack.

Why

Upstream rollback per trunk-io/docs#657 ("we're rolling back the feature for now"). Confirmed with Robert (merge-queue eng) that only the /trunk stack portion needs to be removed; the per-PR /trunk merge flow on the same page is unaffected.

Changes

• merge-queue/using-the-queue/stacked-pull-requests.mdx — rewritten to cover only the per-PR enqueue flow:
  • Frontmatter description updated (drops /trunk stack reference).
  • Intro paragraph rewritten as a single-approach explanation.
  • "Choose your approach" comparison table removed.
  • Entire "Merge the stack as one unit" section removed (Prerequisites, Stack requirements, Command syntax, What happens when you run /trunk stack, The stacked PR, Lifecycle, Why /trunk stack creates a separate PR).
  • "Enqueue each PR individually" content promoted to the page's main flow (Step 1 / Step 2 / Considerations).

Net: 5 insertions, 132 deletions; one file changed.

Test plan

• Preview the page on Mintlify and confirm only the /trunk merge flow renders.
• Confirm no broken anchor links to #merge-the-stack-as-one-unit from elsewhere in the docs.

[samgutentag]

Verification status (2026-05-19): live

Verified: customers can use this. Ready to publish.

• Eng PRs: (Chore): Fix copy on welcome page docs#663 (welcome copy, merged 2026-05-14), Document automatic label application from monitors docs#656 (monitor framework, merged 2026-05-14), Remove stacked PR references docs#657 (remove stacked PR refs, merged 2026-05-13)
• Flag: monitor action framework gated by showLabelActions (true in e2e default)
• Signals: same as PRs [close - superseded by #24] docs: migrate recent changes from trunk-io/docs #13 and [close - superseded by #24] docs: migrate recent updates from trunk-io/docs #23 plus deletion of stacked-pull-requests.mdx (feature rolled back per Remove stacked PR references docs#657: "we're rolling back the feature for now").

Note: PRs #13 and #23 cover overlapping migration scope. This PR is the most complete (includes the stacked-PR rollback). Consider merging this and closing the other two.

[samgutentag]

Catchup check (2026-05-19): partially superseded, one change still needed.

Compared this PR's tree against current main:

• 6 of 7 files (index.mdx, flaky-tests/detection/*.mdx, flaky-tests/management/test-labels.mdx) are byte-identical to main. Those were migrated by PR docs: migrate monitor label actions and welcome copy from trunk-io/docs #24 (merged 2026-05-18, commit 1900ac5).
• The one remaining change is the deletion of merge-queue/using-the-queue/stacked-pull-requests.mdx (from Remove stacked PR references docs#657: "we're rolling back the feature for now"). That file is still present on main.

A clean rebase against current main yields exactly that one deletion:

 merge-queue/using-the-queue/stacked-pull-requests.mdx | 178 ----------------------
 1 file changed, 178 deletions(-)

Options:

1. Rebase this branch onto main (force-push) so the PR reduces to the clean single-file deletion. I tested the rebase locally; it applies cleanly with no conflicts.
2. Close this PR and open a fresh one with just the deletion. Cleaner history but more churn.
3. Cherry-pick the deletion onto a new branch.

Let me know which approach you prefer and I will proceed. Per the no-force-push rule, I have not modified the remote branch.

[samgutentag]

Rebased (2026-05-19). Branch force-pushed onto current main. PR now contains a single commit deleting merge-queue/using-the-queue/stacked-pull-requests.mdx (178 lines). Title and body updated to match. Ready to merge.

[samgutentag]

Reworked (2026-05-19) per Robert's feedback in Slack.

Previous version deleted the whole stacked-pull-requests.mdx file. Robert confirmed only the /trunk stack portion needs removal; the per-PR /trunk merge flow documented on the same page is unaffected.

Branch force-pushed. The PR now contains a single commit that rewrites the page to cover only the sequential-enqueue flow (5 insertions / 132 deletions). Title and body updated to match.