Move the frame dump and GPU capture hotkey to Ctrl+Shift+F7

[athei]

Symptoms

Pressing Ctrl+Shift+F12 in a game did not arm the frame dump and GPU capture. On macOS the Metal Performance HUD library (/usr/lib/libMTLHud.dylib) adds a "Metal HUD" menu to the app's menu bar, and that menu binds Ctrl+Shift+F9, F10, F11 and F12 to "Generate Performance Report" for 5 s, 30 s, 1 min and 5 min. The menu consumes the key before Wine sees it, so the layer never got the press, and in a game test the 5-minute report then crashed the game inside Apple's code.

The same menu also takes Shift+F8 (logging), Shift+F9 (enable HUD), Shift+F11 (reset metrics) and Shift+F12 (configuration panel); its key-down watcher handles Shift+F7 (move HUD) and Shift+F10 (layout), and with MTL_HUD_DISABLE_MENU_BAR=1 Shift+F5, F6, F8, F9 and F12. Plain F12 is Steam's screenshot key, macOS uses Ctrl+F1 to Ctrl+F8 without Shift for focus moves, and F11 for Show Desktop.

Changes

The hotkey is now a fixed Ctrl+Shift+F7: F7 going down while Control and Shift are held and Alt is up (winemac reports either Command key as Alt). The edge semantics are the same as before: a held chord fires once, Control and Shift pressed after F7 is already down never fire, and the modifiers are read only on the present where F7 goes down.

windows/core/src/capture_chord.rs now owns the key codes: CAPTURE_KEY (VK_F7) and Modifier::virtual_key for VK_CONTROL, VK_SHIFT and VK_MENU. windows/d3d9/src/capture.rs drops its local VK_* constants and reads those, and its latch static is renamed from F12_DOWN_LAST to CAPTURE_KEY_DOWN_LAST with its doc-block argument kept.

The unit tests in capture_chord/tests.rs now model each sample as the set of virtual keys held and read the capture key and modifiers by the module's codes, with the codes restated from the Win32 headers so a moved code fails a test. They check that Ctrl+Shift+F7 fires once per press and not while held, and that F7, Shift+F7, Ctrl+F7, Ctrl+Alt+Shift+F7, F12, Ctrl+Shift+F12, the HUD's Shift+F8 to F12 and Ctrl+Shift+F9 to F12, and the near miss Ctrl+Shift+F8 do not.

Every doc and comment that named Ctrl+Shift+F12 now names Ctrl+Shift+F7: the README, docs/ARCHITECTURE.md (section heading and its anchor), the link to it in docs/GAMES.md, CONTRIBUTING.md, the bench-shape text in the Makefile, mtld3d.conf, the bench runner's messages and the code comments on both sides. The README and the architecture section replace the old reason with the actual collisions (Steam's F12 and the HUD's Shift+F8 to F12 and Ctrl+Shift+F9 to F12), keep the Control-not-Command note, and add that a MacBook keyboard needs Fn for F7 unless "Use F1, F2, etc. keys as standard function keys" is on. The mentions of dumps that were taken with plain F12 before the chord existed (the bench_wow112.rs source line and its COVERAGE row, the bench_frame_shape.rs module doc) stay as they are, since they describe how those dumps were made.

Alternatives considered

Keeping F12 with a different modifier set: every Shift and Ctrl+Shift combination on F12 is the HUD's, and plain F12 is Steam's. Ctrl+Shift+F9 to F11 are HUD report keys too. Ctrl+F1 to Ctrl+F8 without Shift are macOS focus moves, and F11 is Show Desktop. Shift+F7 belongs to the HUD's key-down watcher, but the watcher requires Control to be up for it, and the HUD's menu has no F7 entry, so Ctrl+Shift+F7 is not a HUD key; it is not among the macOS shortcuts listed above either, which is why F7 with both modifiers was picked.

A configurable key was not added: the chord stays fixed, with no config key and no environment variable, as before.

Verification

make fmt, make check (rustfmt, clippy with nursery and pedantic on both workspaces and the PE targets, make audit, make doc) and make test-unit ran green: 1970 windows-workspace tests and 755 unix-workspace tests passed, including the 12 capture_chord tests. No end-to-end test uses the hotkey, so make test was not run. The new key has not been pressed in a game yet; a reviewer can check it by pressing Ctrl+Shift+F7 in any game with MTL_CAPTURE_ENABLED=1 and looking for the [dump] lines and a <exe>-<pid>-<n>.gputrace beside the log.

Rules check

The change adds no new static: the existing per-poll latch is renamed, and its doc block keeps the "resource is process-wide" argument from docs/CONVENTIONS.md (State lives on an object, not in a static). It adds no config key, no environment variable, no wire field, no dependency, no derive and no lint suppression. The virtual-key codes move from windows/d3d9 into mtld3d-core rather than being duplicated, which follows "Factor pure functionality into mtld3d-core; d3d9 is wiring"; the tests restate them on purpose as the independent check. The tests stay in capture_chord/tests.rs (Unit tests live in <stem>/tests.rs). Doc blocks keep the title, blank, body shape. make check enforces these through clippy, make audit and make doc, and it ran green.