docs: ADR for InputInjector / sparse-package vision-mode UWP coverage spike

[mvanhorn]

Summary

docs: ADR for InputInjector / sparse-package vision-mode UWP coverage spike

Closes #1552

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Summary by CodeRabbit

• Documentation
  • Added comprehensive README for Windows platform backend, documenting architecture, functionality overview, and known coverage limitations
  • Added detailed Architecture Decision Record covering Windows system integration strategies, evaluated implementation approaches, and deferred roadmap decisions
  • Improved implementation documentation with technical comments clarifying design decisions in click handling fallback logic

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 3010165a-e0ee-4409-b7f9-55897131aced

📥 Commits

Reviewing files that changed from the base of the PR and between 7d893ce and ab12126.

📒 Files selected for processing (3)

• libs/cua-driver/rust/crates/platform-windows/README.md
• libs/cua-driver/rust/crates/platform-windows/src/tools/impl_.rs
• libs/cua-driver/rust/docs/adr/0001-input-injection-tier-decision.md

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📝 Walkthrough

Walkthrough

This pull request documents the architectural decision to defer a Windows InputInjector tier for vision-mode clicks. It adds an ADR explaining the deferral rationale, updates implementation comments to reference the decision, and introduces a README describing platform-specific behavior and known coverage gaps.

Changes

Windows Vision-Mode Click Architecture Decision

Layer / File(s)

Summary

Architecture Decision and Documentation libs/cua-driver/rust/docs/adr/0001-input-injection-tier-decision.md, libs/cua-driver/rust/crates/platform-windows/src/tools/impl_.rs, libs/cua-driver/rust/crates/platform-windows/README.md

ADR-0001 documents the decision to defer InputInjector tier until user-reproducible failing targets justify the sparse-package installer cost. The existing layered approach (UIA InvokePattern + PostMessage fallback) remains default and background-safe, with explicit opt-in foreground routing as a future escape hatch. Implementation comment in ClickTool references this decision, and README documents the known coverage gaps for users.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• trycua/cua#1708: Modifies the background/UIA dispatch flow and coordinate mapping for pixel clicks in the same ClickTool implementation that this PR documents.

Poem

🐰 A rabbit ponders the tower so tall,
Yet settles for wisdom: not reaching at all.
The layered approach holds firm and true,
InputInjector waits for a need that rings through. ✨📋

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: documenting an ADR for InputInjector and sparse-package exploration for vision-mode UWP coverage, which aligns with the PR's primary purpose.
Linked Issues check	✅ Passed	The PR fully addresses issue #1552's acceptance criteria by delivering decision documentation (ADR 0001) that explains the InputInjector / sparse-package evaluation and the decision to defer implementation pending a user-reproducible failing target.
Out of Scope Changes check	✅ Passed	All changes (ADR document, README addition, and explanatory comment) are directly related to documenting the vision-mode click coverage analysis and decision, with no unrelated modifications introduced.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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