[Aschenbath]

Result / 用户结果

Closes #781

When a current Pi workload uses the alternate screen with alternate scrolling enabled and no application mouse reporting, an unmodified wheel event now sends one PageUp/PageDown command instead of cursor arrows. Fractional wheel deltas still accumulate before paging. Existing application mouse reporting takes priority, and other foreground programs retain their existing scrolling behavior.

Design / 设计边界

• The GPUI pointer adapter owns this fallback and uses the shared terminal key encoder, including negotiated Kitty press/release events.
• Reuse the current-program classifier used by Send-to-Chat. Explicit OSC 7501 program identity takes precedence; retained conversation identity cannot page another foreground program.
• No new dependencies, settings, persisted formats, or thread/lifetime changes. The rationale and upstream Pi key-binding evidence are in architecture/notes/nebula_app/gpui_shell/terminal/view/2026-10-31-pi-wheel-paging.md.

Evidence / 验证依据

• cargo test --locked -p nebula --features gpui-test-support --bin pebrel pointer:: -- --test-threads=1: 43 passed.
• cargo test --locked -p nebula --features gpui-test-support --no-fail-fast -- --test-threads=1: 2,725 unit tests passed, 36 ignored, 1 failed; 27 integration tests passed, 1 ignored. The sole failure is git_completion::tests::real_branches_cache_invalidation_and_directory_context (nested release-tag completion), also reproduced in the pre-change test binary. Its source matches origin/main.
• cargo check --locked -p nebula --bin pebrel --features gpui-shell --tests: passed, with warnings in unchanged code.
• cargo clippy --locked -p nebula --all-targets --features gpui-test-support: blocked by 19 existing errors in nebula_terminal. The core source matches origin/main; cargo clippy --locked -p nebula_terminal reproduces the same diagnostics and locations. No lint rules were weakened.
• cargo test --locked -p nebula-settings: 107 passed. The isolated i18n contract suite: 24 passed, 1 ignored.
• cargo fmt --all -- --check, git diff --check, and python3 scripts/check_architecture.py --base 42ffd11ff95db61eacaf026319c0bfb3bed3bea1: passed. The three architecture/governance unittest modules: 55 passed.

Local builds used one Cargo job, disabled incremental compilation and debug information. Two early test builds were killed with SIGKILL during code generation; the completed builds used MALLOC_ARENA_MAX=1 MALLOC_TRIM_THRESHOLD_=0 MALLOC_TOP_PAD_=0, cleared by the Cargo runner for test execution. Clippy was also attempted with a command-line profile.dev.package.nebula.codegen-units=256 override. No build configuration files changed.

The existing pre-fix test binary reproduced the defect: one three-line wheel event emitted three Up-arrow sequences instead of PageUp. The regression dispatches through the real terminal element and covers both directions, one-page batching, fractional accumulation, Kitty encoding, SGR precedence, stale identity, explicit program status, and alternate-screen exit. Routing tests cover mode and modifier exclusions.

The batching assertion observes one transport message per event. Identity normalization and key encoding may allocate; no allocation-free or universal performance claim is made.

Linux validation uses virtual GPUI windows. Live Pi, native macOS-to-Windows SSH, and visual/platform acceptance were not run. This fixes the fallback when mouse reporting is absent; it does not establish why reporting was unavailable in the original SSH connection. Pi owns its internal transcript and scrollbar; the test confirms Pebrel has no local scrollback thumb on that alternate screen.

Required Review / 必须确认

• Followed CONTRIBUTING.md, docs/architecture.md, and docs/project-constraints.md.
• Kept responsibilities cohesive and reused existing behavior authorities.
• Architecture validation passes without budget changes.
• Added regression coverage and stated platform/feature and validation limitations.
• No new UI messages; i18n additions are not applicable.
• No governance rules changed; governance revision requirements are not applicable.