refactor(sdk): simplify CLI completion and display state - #1384

Summary

The CLI tracks child-process completion and terminal updates with state that duplicates existing mechanisms. Remove those extra flags and bookkeeping while preserving completion, cancellation, terminal cleanup, and displayed output.

Changes

Rely on a Promise settling only once for child completion and errors. Use the existing stream-generation counter to identify the active progress session during listener cleanup. Remove redundant dashboard state updates, write frames directly, and use the remaining first-line prefix to track history indentation.

Testing

In the recorded focused run, a real child-process fixture ignores SIGTERM and verifies that CLI cancellation still settles with exit status 143. Writable-stream fixtures inject asynchronous output failures and check that error listeners remain until output settles, then are removed. Dashboard fixtures check terminal restoration after rendering/setup failures, and history fixtures check visible content at narrow and wide widths.

After building the bundled plugin, repeat from sdk/typescript with bun test tests-ts/cli.test.ts tests-ts/cli-skills.test.ts tests-ts/scan-dashboard.test.ts tests-ts/scan-history-renderer.test.ts. The SIGTERM fixture is POSIX-only.

Risk and rollout

No CLI syntax or output-format changes are intended. Completion and stream cleanup must remain correct when events arrive after cancellation or after progress restarts.

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