fix(runtime): port yoga backend to taffy 0.13

[proggeramlug]

Summary

Ports the Perry TUI and Yoga layout backends from taffy 0.7 to 0.13 without an unsafe Send assertion. Yoga nodes now live in a per-thread registry, matching the single-threaded UI runtime and taffy 0.13 storage model.

Changes

• update taffy and its lockfile entry to 0.13
• migrate TUI and Yoga alignment values to the new associated constants
• preserve Yoga’s existing unsafe overflow-alignment semantics explicitly
• move Yoga nodes and the GC scanner-registration latch to thread-local storage so every JS worker registers and scans its own callback roots
• add focused alignment and thread-isolation regression tests

Related issue

Closes #8438

Test plan

• cargo check --locked -p perry-runtime

• cargo test -p perry-runtime --lib yoga::tests -- --test-threads=1

• cargo test -p perry-runtime --lib tui::layout::tests -- --test-threads=1

• cargo fmt --all -- --check

• git diff --check

• ./scripts/pre-tag-check.sh --quick

• cargo build --release clean

• cargo test --workspace --exclude perry-ui-ios --exclude perry-ui-tvos --exclude perry-ui-watchos --exclude perry-ui-gtk4 --exclude perry-ui-android --exclude perry-ui-windows passes

• (if user-facing) Added or updated a test under test-files/ or a #[test] in the affected crate

• (if CLI / stdlib / runtime API changed) Docs are not required; no public API changed

• (if touching a platform UI backend) Built -p perry-ui-<backend> locally on that platform

Checklist

• I have NOT bumped the workspace version or edited CLAUDE.md / CHANGELOG.md (maintainer handles these at merge)
• My commits follow the loose feat: / fix: / docs: / chore: prefix convention used in the log
• I have read CONTRIBUTING.md and agree to the Code of Conduct

Summary by CodeRabbit

• Bug Fixes

  • Updated layout handling to the latest Taffy version while preserving existing alignment behavior.
  • Improved reliability of Yoga-based layouts across worker threads.
  • Added safeguards for alignment and overflow behavior.

• Documentation

  • Added changelog notes covering the layout backend updates.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 1d0bb4a1-a4c6-4b48-a7e7-cde901821d98

📥 Commits

Reviewing files that changed from the base of the PR and between 50245d7 and 523861a.

⛔ Files ignored due to path filters (1)

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

📒 Files selected for processing (4)

• changelog.d/8503-taffy-013.md
• crates/perry-runtime/Cargo.toml
• crates/perry-runtime/src/tui/layout.rs
• crates/perry-runtime/src/yoga.rs

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📝 Walkthrough

Walkthrough

The runtime upgrades Taffy from 0.7 to 0.13, updates alignment constants, and moves Yoga node and GC scanner state from process-wide storage to thread-local storage. Tests cover alignment safety and per-thread registry isolation.

Changes

Taffy and Yoga runtime update

Layer / File(s)	Summary
Taffy 0.13 alignment update crates/perry-runtime/Cargo.toml, crates/perry-runtime/src/tui/layout.rs, crates/perry-runtime/src/yoga.rs, changelog.d/8503-taffy-013.md	The runtime upgrades Taffy to 0.13 and uses its uppercase alignment constants. The changelog records the migration and preserved unsafe overflow alignment.
Thread-local Yoga registry and validation crates/perry-runtime/src/yoga.rs	Yoga node storage and GC registration now use per-thread state. Tests verify alignment safety and independent thread-local registries.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 52386

This localized runtime dependency migration preserves the intended thread-isolated behavior and includes focused regression coverage; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant YogaWorkerThread
  participant YogaNodeRegistry
  participant GCScanner
  participant MeasureCallbacks
  YogaWorkerThread->>YogaNodeRegistry: call with_nodes
  YogaNodeRegistry->>GCScanner: register root scanner once per thread
  GCScanner->>YogaNodeRegistry: scan current thread's nodes
  YogaNodeRegistry->>MeasureCallbacks: scan stored measure callbacks

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Suggested reviewers: thehypnoo

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 36.36% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 2 files. (2 skipped: 2 unsupported.)	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the runtime Yoga backend port to taffy 0.13, which is the primary change.
Description check	✅ Passed	The description includes the required summary, changes, issue reference, test plan, and checklist with clear implementation details.
Linked Issues check	✅ Passed	The changes satisfy all coding requirements in issue #8438, including alignment constants, explicit safety, thread-local storage, and GC root handling.
Out of Scope Changes check	✅ Passed	The reviewed changes are limited to the taffy upgrade, Yoga and TUI migration, tests, and related changelog documentation.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[proggeramlug]

Audited and merging.

This is more than a dependency bump — it also closes a latent multi-thread GC rooting hole, and the PR description undersells that half.

MUTABLE_ROOT_SCANNERS is thread-local (crates/perry-runtime/src/gc/roots.rs:105), but on main GC_SCANNER_REGISTERED is a global Mutex<bool>. So the first thread to touch yoga registers yoga_root_scanner into its own thread-local registry and flips the global latch — and every later thread sees the latch already true and registers nothing. That thread's collector then never scans yoga's stored JS measure callbacks, so a callback set by a second worker between setMeasureFunc and calculateLayout is invisible to the collector that would reclaim it.

Moving both the registry and the latch to perry_thread_local! is the correct fix, and the reasoning in the code comment is right about why the latch has to follow the registry. YOGA_NEXT_ID correctly stays a global Mutex, so handle ids remain unique across the per-thread registries and a stale id cannot alias a live node on another thread.

The port itself is mechanical — associated constants for the alignment enums, grid dropped from the lockfile. Good call pinning AlignmentSafety::Unsafe on every mapped alignment with an explicit assertion rather than inheriting whatever taffy 0.13 defaults to; that is the kind of behavior an enum-shape migration silently flips.

Validation on this branch:

check	result
gc_runtime_root_holders gate	OK — 633 holders, 96 scanner-reached, 140 registered scanners
yoga:: tests (incl. yoga_registry_and_gc_registration_are_per_thread)	2 passed
tui::layout tests	6 passed
perry-runtime --lib, RUST_TEST_THREADS=1	2608 passed, 4 ignored

One consequence worth a line in the changelog: a yoga node created on one thread is no longer visible from another. That is consistent with the single-threaded UI runtime the handle design assumes, and the new isolation test pins it — but it is a real behavioral narrowing, not just an internal refactor.