feat(ui): wire GC pump-step + OS memory-pressure into non-macOS hosts (#6183, #6184)

[proggeramlug]

Extends the GC embedder integration already merged for the macOS host to the
remaining UI hosts. Two runtime FFIs land on main already; this wires the
host-side calls. Reference: #6183 #6184; 2026-07-09 GC audit.

A. Pump GC-step (#6183)

Mirrors the merged macOS pump call: js_gc_step_us(2_000, null) in each host's
run-loop / timer pump tail. That point is a precise-root safepoint (the JS
stack is fully unwound), so an active budgeted GC cycle drains in bounded 2ms
slices instead of an unbounded alloc-point collection landing on the UI thread
mid-interaction. Extern declared per host, matching the macOS style.

Host	Pump site
iOS	PerryPumpTarget::pump: (perry-ui-ios/src/app.rs)
tvOS	PerryPumpTarget::pump: (perry-ui-tvos/src/app.rs)
visionOS	PerryPumpTarget::pump: (perry-ui-visionos/src/app.rs)
watchOS	SwiftUI render Timer in PerryWatchApp.swift (@_silgen_name FFI)
gtk4	glib::timeout_add_local pump closure (perry-ui-gtk4/src/app.rs)
Windows	Win32 message-loop TIMER_TICK_NEEDED block (perry-ui-windows/src/app.rs)
Android	nativePumpTick JNI callback (perry-ui-android/src/app.rs)

B. OS memory-pressure (#6184)

Forwards the platform signal to js_gc_memory_pressure(level) (1 = minor,
2 = full collect + trigger clamp).

• iOS / tvOS — added applicationDidReceiveMemoryWarning: to the Rust
  PerryAppDelegate (define_class!), calling js_gc_memory_pressure(2) (a
  UIKit memory warning is the last notice before jetsam → critical).
• visionOS — the SwiftUI host has no app-delegate memory callback, so
  PerryVisionBootstrap observes UIApplication.didReceiveMemoryWarningNotification
  on the main queue → level 2.
• macOS — new memory_pressure.rs installs a
  DISPATCH_SOURCE_TYPE_MEMORYPRESSURE source on the main queue at app_run:
  WARN → 1, CRITICAL → 2. libdispatch symbols bound directly (part of
  libSystem; no new crate). This is the one macOS piece that wasn't done yet.
• Android — PerryActivity.onLowMemory() → 2; new onTrimMemory(level)
  override maps TRIM_MEMORY_RUNNING_CRITICAL | COMPLETE | MODERATE → 2 and
  lighter trims → 1 (constants aren't monotonic by severity, so the severe set
  is matched explicitly). Wired via a new nativeMemoryPressure JNI shim
  (perry-ui-android/src/lib.rs) + Kotlin external fun (PerryBridge.kt),
  guarded against UnsatisfiedLinkError for warnings that arrive pre-init. The
  existing Google-Maps forwardMapsLifecycle("lowMemory") is preserved.

Out of scope

• Linux PSI polling for gtk4 — a server concern, deliberately not added.
• Windows / gtk4 OS memory-pressure — no in-scope UI memory signal was
  wired (only the pump-step). Notable as remaining if desired later
  (WM_COMPACTING / QueryMemoryResourceNotification on Windows).

Build verification

Verified with target-specific cargo check where the toolchain is present;
inspection-only where a cross native-toolchain is missing on this macOS host
(honest status — no fabricated builds):

Host	Build-verified?
macOS	cargo check -p perry-ui-macos — PASS (includes dispatch-source module)
iOS	cargo check --target aarch64-apple-ios — PASS
tvOS	cargo check --target aarch64-apple-tvos — PASS
visionOS	cargo check --target aarch64-apple-visionos — PASS (Rust; Swift template inspection-only)
watchOS	Rust crate PASS; the change is Swift-only (PerryWatchApp.swift), inspection-only
gtk4	inspection-only — cross-compile blocked (glib-sys pkg-config can't cross-compile)
Windows	inspection-only — cross-compile blocked (libmimalloc-sys needs a Windows C++ toolchain)
Android	inspection-only — cross-compile blocked (aarch64-linux-android-clang NDK not installed); Kotlin inspection-only

cargo fmt --all -- --check passes.

Summary by CodeRabbit

• New Features
  • Added improved memory-pressure handling across supported platforms, helping the app respond more quickly to low-memory situations.
  • Added incremental background runtime cleanup during regular UI/update cycles to spread work into small bounded steps.
• Bug Fixes
  • Reduced the chance of sudden performance spikes by avoiding larger cleanup bursts during normal app activity.
  • Improved stability when the operating system sends memory warning signals.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 819b9ec9-1632-42c8-8865-9947996c0559

📥 Commits

Reviewing files that changed from the base of the PR and between d9500be and 27a2c4a.

📒 Files selected for processing (14)

• crates/perry-ui-android/src/app.rs
• crates/perry-ui-android/src/lib.rs
• crates/perry-ui-android/template/app/src/main/java/com/perry/app/PerryActivity.kt
• crates/perry-ui-android/template/app/src/main/java/com/perry/app/PerryBridge.kt
• crates/perry-ui-gtk4/src/app.rs
• crates/perry-ui-ios/src/app.rs
• crates/perry-ui-macos/src/app.rs
• crates/perry-ui-macos/src/lib.rs
• crates/perry-ui-macos/src/memory_pressure.rs
• crates/perry-ui-tvos/src/app.rs
• crates/perry-ui-visionos/src/app.rs
• crates/perry-ui-visionos/swift/PerryVisionApp.swift
• crates/perry-ui-watchos/swift/PerryWatchApp.swift
• crates/perry-ui-windows/src/app.rs

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📝 Walkthrough

Walkthrough

This PR adds a bounded embedder GC step (js_gc_step_us, 2ms budget) invoked at each UI pump tick across Android, GTK4, iOS, tvOS, visionOS, watchOS, and Windows, and wires OS memory-pressure signals (Android JNI, iOS/tvOS memory warnings, macOS libdispatch source, visionOS notifications) into js_gc_memory_pressure.

Changes

Embedder GC pump-step and memory-pressure wiring

Layer / File(s)	Summary
Android GC step and memory pressure crates/perry-ui-android/src/app.rs, crates/perry-ui-android/src/lib.rs, crates/perry-ui-android/template/.../PerryActivity.kt, crates/perry-ui-android/template/.../PerryBridge.kt	Adds js_gc_step_us call in the pump tick, a nativeMemoryPressure JNI bridge, and Kotlin onLowMemory/onTrimMemory handlers forwarding memory pressure levels.
GTK4 pump GC step crates/perry-ui-gtk4/src/app.rs	Adds js_gc_step_us FFI declaration and a bounded step call in the main pump tick callback.
iOS memory warning and pump GC step crates/perry-ui-ios/src/app.rs	Adds applicationDidReceiveMemoryWarning: handler, js_gc_step_us/js_gc_memory_pressure FFI bindings, and a per-tick GC step in PerryPumpTarget.
macOS libdispatch memory-pressure source crates/perry-ui-macos/src/lib.rs, crates/perry-ui-macos/src/memory_pressure.rs, crates/perry-ui-macos/src/app.rs	Adds a new memory_pressure module installing a libdispatch source that maps WARN/CRITICAL flags to js_gc_memory_pressure calls, wired into app_run startup.
tvOS memory warning and pump GC step crates/perry-ui-tvos/src/app.rs	Adds applicationDidReceiveMemoryWarning: handler and a bounded js_gc_step_us call in the pump loop.
visionOS pump GC step and memory warning crates/perry-ui-visionos/src/app.rs, crates/perry-ui-visionos/swift/PerryVisionApp.swift	Adds js_gc_step_us pump invocation in Rust and a Swift memory warning observer calling js_gc_memory_pressure.
watchOS pump GC step crates/perry-ui-watchos/swift/PerryWatchApp.swift	Adds js_gc_step_us FFI declaration and a per-frame GC step call in PerryBridge.start().
Windows pump GC step crates/perry-ui-windows/src/app.rs	Adds js_gc_step_us FFI declaration and a bounded GC step call in TIMER_TICK_NEEDED handling.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related issues

• [gc] React to OS memory pressure: didReceiveMemoryWarning / onTrimMemory / PSI / dispatch_source adapters #6184: Implements the same OS memory-pressure GC plumbing (js_gc_memory_pressure) across Android/iOS/macOS/tvOS/visionOS described in the issue.
• [ui] Wire js_gc_step_us into UI run loops — GC pauses currently land mid-frame on the main thread #6183: Implements the js_gc_step_us UI run-loop wiring described in the issue across perry-ui hosts.

Possibly related PRs

• PerryTS/perry#5973: Both PRs modify the watchOS PerryWatchApp.swift per-frame PerryBridge.start() tick logic, with this PR adding an additional js_gc_step_us call in the same timer boundary.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the GC pump-step and memory-pressure wiring across UI hosts, though it omits the macOS memory-pressure addition.
Description check	✅ Passed	The description is detailed and on-topic, covering summary, changes, related issues, and verification, though it does not follow the repository template exactly.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/ui-gc-platform-integration

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