wasm: separate browser text commits, IME composition and keyboard shortcuts

[subinium]

Priority: P2
Evidence: Trusted Chrome Cmd+V reproduction; physical OS IME remains untested
Baseline: v0.23.0 source 37933f9, audited 2026-09-05. Native execution/compile probes used Rust 1.98.0 on aarch64 macOS unless explicitly stated otherwise.

Problem and Reproduction

A paste listener exists, but every recognized keydown is prevented, including Cmd/Ctrl+V. In a controlled Chrome clipboard test a plain focusable host receives1 paste, while the current cancellation policy receives0. There is no composition/beforeinput/input bridge; synthetic composing Enter is treated as a normal key. Synthetic composition is not proof of physical Korean/Japanese IME behavior.

crates/slt-wasm/src/lib.rs:476 · crates/slt-wasm/src/lib.rs:717 · crates/slt-wasm/src/lib.rs:894

Scope

• Preserve native paste generation and commit browser text exactly once.
• Separate navigation/shortcuts from composition and input commits; add a focused editable sink if needed.
• Define focus ownership, caret placement and browser copy/cut capability boundaries.

Expected Effect

Make normal paste and multilingual browser text entry usable without accidental form submission or duplicated characters.

Acceptance Criteria

• Trusted shortcut paste and context-menu paste produce identical content once.
• Record physical Korean/Japanese IME, dead keys, emoji, cancellation and confirming Enter behavior.
• No double insertion across keydown/input and no intermediate composition keys delivered as commands.
• Two mounts plus a normal page input preserve outside browser shortcuts and focus transfer.
• Follow the repository quality gates and the evidence rules in tracking: post-v0.23 correctness, resource efficiency and WASM completion #366; record actual results rather than treating a proposed test as passed.

Boundaries and Dependencies

Do not request arbitrary clipboard-read permission as a paste fix. Existing OSC52 copy API is terminal-specific, not a broken browser clipboard promise.

• wasm: replace unsupported time sources on the browser frame path #403
• wasm: share stable cell geometry between DOM rendering, resize and hit testing #405
• input: preserve the original order of paste and key events #373
• input: compute caret and length limits from the resulting grapheme sequence #421

Related closed work: #298. This is a scoped follow-up at the audit baseline, not a claim that every prior fix is absent.

Tracking: #367; overall audit #366. This issue records unresolved work, not an implemented fix.

[subinium]

v0.24.0 Disposition

The published text bridge passes trusted paste/typing, exactly-once commits, no composing Enter leak, focus isolation, visible preedit and teardown. A reproduced masked-preedit leak and a pre-frame masking race are fixed using explicit rendered-caret privacy and fresh-frame-only painting. The exact registry consumer passed all 15 Playwright scenarios and 10 compiled integration tests on Linux and macOS. Physical Korean/Japanese IME, native context-menu UI and mobile soft keyboards remain untested. Stop was not reproduced as a bug before the preedit change; trusted post-Stop typing is verified ignored. Distinct Korean glyph pixels are tested with CJK fonts, not counted as physical OS composition evidence.

Implementation and evidence mapping: PR #433. Release v0.24.0 and its 20/20 release workflow are verified. This issue stays open only for the remaining acceptance/investigation described above; publication alone does not establish it.