perf(codemode): cache unchanged rendered frames

[dnlrsls]

Linked issue

Refs #2017

PR type

• Bug fix
• New feature
• Documentation only
• Code refactoring
• Maintenance/tooling
• Breaking change

Summary

• Reuse a single rendered frame per Codemode card when normalized width, card style and computed running state are unchanged.
• Clear cached frames on component invalidation; result arrival still recomputes the running call frame.
• Preserve exact ANSI output and fresh partial, final and expanded components without changing shared wrapping or execution.

Changes

File	Change
lib/codemode-renderer.ts	Single-entry per-component rendered-frame cache and invalidation.
tests/codemode-rendering.test.ts	Four public-renderer regressions for reuse, layout/theme changes, result transitions and content freshness.

Test plan

• RED observed against the original renderer: unchanged renders duplicated painting (22 vs 11).
• node --experimental-strip-types --test tests/codemode-rendering.test.ts tests/quiet-tool-rendering.test.ts tests/shell-card.test.ts: 127 passed, 0 failed.
• Independent verifier: node --experimental-strip-types --test tests/codemode-rendering.test.ts: 32 passed, 0 failed.
• pnpm typecheck: zero diagnostics in the local working tree.
• git diff --cached --check: passed before commit.
• Native assessment of this committed range: medium; reviewDue=false.
• Full package suite is not locally approved: the Windows run produced failures in other areas and was stopped without a final summary. These failures were not all classified as baseline.
• Whole-session latency, long-running retention and a Linux baseline/candidate run were not measured. CI remains pending.
• ShellCheck and changed-skill checks: not applicable; no scripts or skills changed in this PR.

Scope

Only commit 18ee9511a is included (two files, 117 additions / 4 deletions). Separate Windows fixture and launcher-timeout changes remain uncommitted locally and are excluded. This cache removes repeated layout work, not first-render cost or the source of render requests.

Contributor checklist

• Linked issue has status:approved.
• Exactly one PR type selected; matching type:bug label requested.
• Conventional commit with tests alongside behavior; no Co-Authored-By trailer.
• Applicable focused and independent checks observed.
• No public command, option, message or configuration contract changed.
• Required CI passed.

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📥 Commits

Reviewing files that changed from the base of the PR and between 563fede and 18ee951.

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📒 Files selected for processing (2)

• lib/codemode-renderer.ts
• tests/codemode-rendering.test.ts

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