docs(markdown): refresh merged-main performance contract

[dowdiness]

Summary

• rerun the checked-in full-parse stage matrix on merged main after perf(markdown): avoid per-code-block document reconstruction #855
• record the updated paragraph and mixed-corpus JS/wasm-gc observations
• mark the mixed 50 ms objective as locally met while keeping the paragraph 10 ms objective open
• stop further cold-path design until a smaller causal benchmark reproduces work inside grammar/event/CST construction
• identify Markdown: derive Block/Inline editor projection from MarkdownIR #332 as the next measured Markdown performance step

Results

Workload	JavaScript	wasm-gc
paragraph-v1 source to Block	11.76 ± 0.32 ms	10.12 ± 0.25 ms
mixed-v1 2k source to Block	35.32 ± 13.95 ms	22.73 ± 6.27 ms
mixed 10k source to Block	102.43 ± 8.27 ms	87.14 ± 4.14 ms

The merged-main mixed result is below the directional 50 ms JavaScript objective and agrees with the cleaner 18.76 ± 2.54 ms post-#855 observation already recorded. The paragraph result remains narrowly outside its 10 ms objective; the largest isolated stage is pretokenized grammar/event/CST construction.

Validation

• rtk bash check-docs.sh
• rtk git diff --check
• Slopless review saved under the ignored .slopless/findings/ workspace directory

Decision record updated: docs/decisions/2026-08-03-markdown-full-parse-performance-contract.md.

Related: #332, #845, #855

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📥 Commits

Reviewing files that changed from the base of the PR and between 9edd23c and 76b8117.

📒 Files selected for processing (3)

• docs/decisions/2026-08-03-markdown-full-parse-performance-contract.md
• docs/performance/benchmark_history.md
• docs/performance/markdown-full-parse-contract.md

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