docs(plan): re-sync the engine plan and fix two colliding changelog fragment numbers

[proggeramlug]

Documentation and metadata correctness only — no code changes.

1. The plan's headline numbers were stale

docs/engine-plan.md still listed the two worst rows of the v0.5.1299 sweep at
their pre-fix values. Both have since moved by an order of magnitude:

kernel	plan said	actually	landed
object_deep_clone	657.0 ms, 37.5x bun	40 ms, ~2.3x bun, 0.67x node (a win)	#7540 (closes #7533)
map_1m	1233.7 ms, 4.8x bun	309.1 ms, 1.40x bun, 0.96x node (a win)	#7561

field_access's standing inversion — the optimized configuration being 2.2x
slower than the unoptimized one — is also closed (#7537 then #7539): 2984 ms
sigma 136 becomes 1809 ms sigma 17.3, and turning the tape on is no longer
worse than turning it off.

Why this matters enough to be its own PR. Three times this campaign a ticket
was picked up and profiled from a headline number that had already collapsed —
#7510 (33.6% → 11%), layout_forget_object (14.5% → 3.0% → 1.7%), and
layout_note_slot (7.5% → 0.03%, correctly closed with no code at all).
A stale plan is not a cosmetic problem; it is how effort gets spent on a
non-problem. The re-synced section now says so explicitly, in place.

The v0.5.1299 table is kept intact rather than overwritten. It was one
measurement event with 11 runs per cell; the fixes were each measured
individually as part of the change that made them. Splicing individually
measured rows into a sweep table would silently claim a coherence the numbers
do not have. Fixed rows are annotated and the deltas live in a section below,
attributed to the PR that moved them.

Also records #7566's landing (workstream A of #7469) and the Mach-O
local-exec TLS negative result, so neither is re-derived.

2. Two changelog fragments collided with real PR numbers

The convention in CLAUDE.md is changelog.d/<PR>-<slug>.md, and it exists
precisely so in-flight PRs never collide. Two fragments were named with an
issue number instead, landing on PR numbers that belong to different changes:

fragment	claimed	actually	real owner of that number
iterator-no-silent-truncation	7565	7567	#7565 is the TLS/_tlv_get_addr change
macos-gap-snapshot-fallback	7566	7568	#7566 is the inline bump allocator

Both misnamed fragments are mine. Left alone, scripts/cut_release_notes.sh
folds them into the release notes under the wrong PR, and the two genuinely
distinct changes sharing a number make the release notes unreadable at exactly
the moment nobody can check them any more.

The general lesson, which is why the naming rule is worth enforcing: a fragment
written before its PR exists has to guess the number. The fix is to open the
PR first and name the fragment from the assigned number — which is what this PR
itself does.

Validation

scripts/check_file_size.sh clean (engine-plan.md is 319 lines against the
2000 cap). No code touched, so no build or test surface is affected. CI has a
deep backlog and may not report; this is a docs-only change.

[coderabbitai]

Warning

Review limit reached

@proggeramlug, you've reached your PR review limit, so we couldn't start this review.

Next review available in: 6 minutes

You've used all free OSS reviews for now. Wait for the free limit to reset to keep reviewing this public repository.

How can I continue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based reviews.

How do review limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan review availability.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, additional reviews become available more gradually as earlier reviews age out of the rolling window.

Please refer docs for additional details.

Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: b77336fb-5d23-461a-8bba-147dc8420730

📥 Commits

Reviewing files that changed from the base of the PR and between b4694a5 and ca7173a.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (6)

• CLAUDE.md
• Cargo.toml
• changelog.d/7567-iterator-no-silent-truncation.md
• changelog.d/7568-macos-gap-snapshot-fallback.md
• changelog.d/7572-plan-resync-fragment-numbers.md
• docs/engine-plan.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/7572-plan-resync-fragment-numbers

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}