fix(computer): make every action invocable (schema field gaps) + element_at/error-mapping fixes

[1jehuang]

Summary

Exhaustively exercised every computer tool action against the live running server and fixed every failure so the tool is production-ready. The handlers were already implemented; the bugs were in the function-calling contract and a few AppleScript/error-mapping/perf details. All fixes are validated live after build + reload.

Fixes #350.

Bugs fixed

1. Schema omitted half the input fields → 8+ actions were impossible to call

ComputerInput deserializes dx, dy, to_x, to_y, w, h, menu_path, window_id, ax_action, contains, timeout_ms, region, level and dispatch() requires them, but parameters_schema() only declared a subset. A model can only emit parameters present in the tool schema, so those fields could never be sent and each dependent action dead-ended in its own requires X guard:
scroll, drag, resize_window, select_menu, window_screenshot, wait_for, set_brightness, perform_action, plus the ocr region variant.

Fix: declare all input fields (action specs stay in discover; fields must be declared). Trimmed descriptions so the always-on schema stays ~880 tokens. Added schema_declares_every_input_field regression test.

2. element_at used the AppleScript reserved word result

result holds the last command's value, so element_at always failed with The variable result is not defined. Renamed to bestHit.

3. element_at walked the entire AX tree → 20s timeout on big apps

Now prunes to only descend subtrees whose frame contains the point (a child's frame ⊆ its parent's), with a depth bound + explicit 12s timeout. Full-tree walk → path-length walk. Live: System Settings used to time out (20s); a comparable large tree (Messages) now returns in ~1.6s.

4. -1719 misclassified as "Accessibility permission required"

-1719 (errAEIllegalIndex) / -1728 (errAENoSuchObject) mean the target reference didn't resolve (app not running / no front window / AX path out of range), not a permission problem. Extracted a pure, unit-tested classify_osa_error: permission text first, then map index errors to an accurate "target not found" message. Use -25211 (errAXAPIDisabled) for the real permission code.

5. wait_for ignored its own timeout_ms

Each poll dumped the AX tree (depth 10) under the 20s default scripting timeout, so a single poll could take ~20s and a timeout_ms=2000 call wouldn't return until ~20s. Now each poll is bounded by the time remaining (capped 3s) and the dump depth is reduced. Live: a 2000ms wait_for now returns in ~2.2s.

Validation

• cargo test -p jcode-app-core --lib tool::computer: 26 passed, 0 failed (10 new tests across the fixes).
• Built selfdev, installed, reloaded the running server through 4 iterations, and re-ran the full action matrix live. Every previously-broken action now works:
  scroll ✓ drag ✓ resize_window ✓ select_menu ✓ (View > Actual Size in Preview) window_screenshot ✓ (captured an occluded window) wait_for ✓ (honors timeout) set_brightness ✓ (clean message) perform_action ✓ (AXPress) ocr region ✓ element_at ✓ (fast + accurate not-found errors).

Notes / known limitations

• wait_for/ui/element_at operate on front window of frontApp; apps on another Space or with non-AX content (Catalyst/Electron/rich-text) expose limited text. This is an inherent AX limitation, not a tool bug. Follow-up tracked in computer tool: truthful observability animation for background AX actions (highlight when visible, notice when occluded) #348.

Test plan for reviewers

cargo test -p jcode-app-core --lib tool::computer
# live (mutates desktop; needs GUI + Accessibility/Screen Recording):
cargo test -p jcode-app-core tool::computer::coverage -- --ignored --nocapture --test-threads=1