fix(shell): finish commands when code cells are killed

[clabby]

Summary

• associate yielded code-mode cell IDs with their original transcript workflow
• when a wait confirms Script terminated, fail that cell's unfinished nested tools and clear their running shell bookkeeping
• retain cell ownership across nonterminal failed waits, including Nanocodex's observer-busy Script failed response
• add regression coverage for a failed wait followed by termination of an unfinished shell command

Testing

• cargo test -p tact tui::transcript::model::tests
• just check-fmt
• cargo check
• just clippy

Stack

Depends on #191.

[codspeed-hq]

Merging this PR will not alter performance

✅ 18 untouched benchmarks
⏩ 31 skipped benchmarks¹

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_{Comparing cl/shell-kill-cleanup (d11219a) with cl/release-0.6.7 (fb706ab)}

Footnotes

1. 31 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩