feat(direct-mode): context awareness — seed from target field + clipboard bridge (RFC 0015)

[willwade]

Summary

Implements the frontend half of the RFC 0015 context-awareness amendment for Windows (governance PR #37; research in #50; engine CAPI in DasherCore PR #83 — submodule pinned to that branch pending merge/tag).

Dasher 5's "direct mode knows the context" was really a session shadow buffer — it never read the target field. This PR restores that parity and exceeds it: predictions now continue from text already in the target field, which v5 never could.

Context seeding (RFC 0015 tiers 1–3)

• TargetContextReader (Services/TargetContextReader.cs): reads the focused control's text + caret via UI Automation TextPattern (modern apps: WPF, UWP, browsers, Office, Electron) with a WM_GETTEXT/EM_GETSEL fallback for classic EDIT/RichEdit controls (Notepad, dialogs). All reads run on a background thread with a 300 ms hard budget — an unresponsive provider can never stall a mode switch; failures return null.
• Seeding triggers:
  • Keyboard-mode entry — reads the field you were typing in, so predictions continue mid-sentence
  • Target-window change — switching fields re-reads and re-seeds the new field (better than v5, which reset to empty); read failure degrades to empty seed (v5 parity, never a dead mode)
• Caret conversion: UIA reports UTF-16 code units; the engine wants UTF-8 bytes — converted with the new dasher_byte_offset_from_utf16 CAPI (the shared, tested converter from DasherCore #83), so CJK/accented text anchors correctly
• 150 ms debounce for focus churn; KbLog traces each seed

Clipboard bridge (mini-bar)

Four new buttons on the keyboard-mode mini-bar:

• Copy — engine buffer → system clipboard
• Cut / Paste / Select-All — Ctrl+X/V/A chords injected into the target via SendInput; they act on the target's selection, which only the target can do — the same reason v5 implemented them frontend-side rather than in control mode

Verification

• Build green, 77/77 tests
• Needs a manual pass: type into Notepad (fallback path), a browser textarea (UIA path), switch between two apps (re-seed), non-ASCII text (conversion), the four mini-bar buttons

Depends on

• DasherCore PR #83 (dasher_seed_buffer, dasher_set_offset, unit converters) — submodule pinned to feat/context-capi; re-pin to the tagged release before merge

Type of change

• New feature (cross-platform parity + capability v5 lacked)

Definition of Done

• Build + tests green
• Commits signed off (DCO)

Greptile Summary

The PR adds target-field context seeding and clipboard controls for direct keyboard mode, with centralized target-window tracking and ownership checks.

• Reads focused-field text and caret positions through UI Automation with a Win32 edit-control fallback.
• Re-seeds predictions on foreground and same-window focus changes.
• Adds Copy, Cut, Paste, and Select-All controls to the keyboard mini-bar.
• Adds target-window identity and UI regression tests.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/Dasher.Windows/Services/TargetContextReader.cs	Adds bounded target-context reads, ownership validation, and layered caret discovery; the latest rcCaret fix resolves the previously reported cross-thread caret-coordinate defect.
src/Dasher.Windows/Services/KeyboardTargetTracker.cs	Centralizes rooted target tracking, focus and foreground hooks, stale-event handling, and foreground restoration.
src/Dasher.Windows/Services/TargetWindowIdentity.cs	Defines and tests a shared GA_ROOT-based target ownership predicate.
src/Dasher.Windows/Views/MainWindow.axaml.cs	Integrates debounced context seeding, generation invalidation, target tracking, and clipboard bridge actions.
src/Dasher.Windows/Views/MainWindow.axaml	Adds keyboard mini-bar controls for copying engine text and sending target-side Cut, Paste, and Select-All commands.

Sequence Diagram

sequenceDiagram
  participant W as WinEvent hooks
  participant T as KeyboardTargetTracker
  participant M as MainWindow
  participant R as TargetContextReader
  participant E as DasherCore
  W->>T: Foreground or focus event
  T->>T: Root and validate target HWND
  T->>M: TargetChanged
  M->>M: Debounce and generation check
  M->>T: Verify target foreground
  M->>R: ReadAsync(target HWND)
  R->>R: UIA TextPattern or Win32 fallback
  R-->>M: Text and UTF-16 caret
  M->>E: Convert caret to UTF-8 offset
  M->>E: Seed buffer

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_{Reviews (19): Last reviewed commit: "fix(keyboard): caret rect from GUITHREAD..." | Re-trigger Greptile}

[willwade]

Structural response to the review series (9c70336): the eight P1s converged on a single invariant — a handle/element belongs to the target iff GA_ROOT lands on the tracked root — so it now exists in exactly one place instead of being re-derived per site:

• TargetWindowIdentity — the one ownership predicate (RootOf/IsOwnedBy)
• KeyboardTargetTracker — hooks, the rooted target HWND, and foreground restoration extracted from MainWindow; the window only decides what to seed
• TargetContextReader — every acquisition path routes through the identity class
• TargetWindowIdentityTests — real Win32 windows: child→root acceptance, sibling-top-level rejection (the case PID gates missed), child-handle rooting, self-ignoring