docs(changelog): merge queue stacked PRs via /trunk stack

[samgutentag]

What shipped

Comment /trunk stack on any PR in a dependent chain (each PR's base is the PR below it) and Trunk combines the chain into one stacked PR the queue tests and merges as a single unit. When the stacked PR merges, every member PR auto-closes.

Source

• Eng PRs: trunk-io/trunk2#3122, #3430, #3490, #3694, #3696, #3707, #3751, #3798
• Linear: TRUNK-18069 (no absorbed duplicates)
• Date basis: 2026-04-30 = latest source PR mergedAt (#3798)

Wired into all 4 sites

• changelog/2026-04-30-merge-queue-stacked-prs-trunk-stack.mdx (new entry)
• docs.json (Changelog tab, 2026 group)
• changelog/index.mdx (April 2026 section)
• merge-queue/changelog.mdx (April 2026 section)

Note

Ticket is tagged [feature not live]. The existing docs page merge-queue/using-the-queue/stacked-pull-requests currently documents the older sequential /trunk merge per-PR flow, not the new /trunk stack single-unit command. Linked as the closest existing page; the page needs an update once the feature is live. Kept as draft pending eng confirmation.

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[samgutentag]

Code verification (2026-05-28): 6 confirmed / 0 contradicted / 0 ambiguous / 0 unverifiable

Claim	Verdict	Source
/trunk stack is the command	confirmed	controller/utils/index.ts
A stack is a chain where each PR's base is the PR below	confirmed	stacked_pr_comment.test.ts:309
A "Stacked" pill marks stacked PRs in Queue/Graph views	confirmed	trunk2#3430 diff (<span>Stacked</span>)
The merge item detail page lists every member PR	confirmed	trunk2#3430 diff (memberPrs -> #{member.prNumber} / {member.prTitle})
Stack-specific cancellation reasons appear in the conclusion chart	confirmed	trunk2#3122 ClickHouse migration add_stacked_pr_cancellation_reasons
Member PRs resolve when the stacked PR merges	confirmed	merge-types/index.ts (STACKED_PR_MEMBER_MERGED)

No contradictions. Every factual claim in the entry matches source. The entry deliberately omits internal terminology (--force, StackedPrMember, trunk-stack/ branch prefix) per the ticket's writer guidance, so there are no claims to over-verify there.

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Source #1 — `/trunk stack` command (confirmed)

File: trunk-io/trunk/trunk/services/merge/src/controller/utils/index.ts

The command string is defined and parsed by the merge controller. Tests assert parseCommand("/trunk stack") and the integration suite drives '/trunk stack --title "..."'. The browser-extension constant TRUNK_STACK_COMMENT = "/trunk stack" matches.

Source #2 — stack is a dependent chain (confirmed)

File: stacked_pr_comment.test.ts#L309

reacts with -1 when the PR directly targets the merge branch (single-PR, not a stack) confirms a stack requires each PR's base to be another PR in the chain, not the merge branch directly. The test also builds a 2-member group, matching the "chain of dependent PRs" framing.

Source #3 — "Stacked" pill (confirmed)

File: trunk-io/trunk2#3430 diff

The PR adds <span>Stacked</span> to the Queue/Graph item rendering. This is the pill referenced in the entry.

Source #4 — member PR list on detail page (confirmed)

File: trunk-io/trunk2#3430 diff

The merge item detail page maps stackedPrGroup.memberPrs to render #{member.prNumber} and {member.prTitle} for each member, backed by the StackedPrMemberInfo GraphQL type.

Source #5 — stack-specific cancellation reasons (confirmed)

File: trunk-io/trunk2#3122 ClickHouse migration V20260302000000__add_stacked_pr_cancellation_reasons.sql

Adds STACKED_PR_MEMBER_PUSHED_TO, STACKED_PR_MEMBER_CLOSED, STACKED_PR_MEMBER_MERGED, STACKED_PR_MEMBER_BASE_BRANCH_CHANGED to merge_item_state_transition. These power the stack-specific reasons broken out in the conclusion chart.

Source #6 — member PRs resolve on stack merge (confirmed)

File: trunk-io/trunk/trunk/services/merge-types/index.ts (STACKED_PR_MEMBER_MERGED)

The STACKED_PR_MEMBER_MERGED cancellation reason is the terminal state for a member PR whose code reached the target branch via the stacked PR. This is the mechanism behind "every member PR auto-closes since its code is already in the target branch."

[samgutentag]

Verification status (2026-06-25): pending

Eng merged but flag off in prod. Hold off.

• Flag state: read directly from LaunchDarkly (production: OFF; test: OFF). enabledMergeQueueStackedPrs has on=false in both environments.
• Eng PR: trunk-io/trunk2#3122, #3430, #3490, #3694, #3696, #3707, #3751, #3798 (all merged; #3798 merge commit on main)
• Flag: enabledMergeQueueStackedPrs (project frontend-web-2)
• Signals: LD direct read (primary). Flag is off in both prod and staging, so the /trunk stack single-unit flow is not reachable by customers yet.

Recommendation: keep held. Re-run once the flag turns on in prod.

[samgutentag]

Docs PR Verify · 2026-06-26

Verdict: pending 🔴

Feature flag enabledMergeQueueStackedPrs is OFF in both test and production. Waiting for flag to be enabled before this feature can ship.

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Daily sweep · 2026-06-26

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