docs(engine-plan): step 7 is a measured backlog; sequence the JSON workstream

[proggeramlug]

Step 7 cited two traps that are both resolved (#7395 closed, #7396 closed as fixed-by-#7421). It now carries the measured backlog from the 2026-08-06 public-baseline sweep, worst-first vs bun, with the JSON workstream sequenced behind its correctness gate — #7477 before #7478 — the roundtrip win to protect (194 ms vs bun 221), and the measured dead ends recorded so they are not re-walked.

Explicitly noted as parallel with the GC-correctness layers: no dependency in either direction, and agent-delegable because every claim checks against the node oracle (PERRY_JSON_TAPE=0/1 checksum parity).

Summary by CodeRabbit

• Documentation
  • Updated the engine performance plan with a measured backlog based on public benchmark results.
  • Added prioritized performance gaps and sequencing for JSON-related improvements.
  • Documented correctness, checksum parity, and quiet-host measurement requirements.
  • Clarified that the JSON workstream is independent of garbage-collection correctness work.
  • Added a changelog entry summarizing the planning updates.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: feec3aec-58fc-4a4b-8f5b-10cf5129b25d

📥 Commits

Reviewing files that changed from the base of the PR and between c1f0b6f and 85bc029.

📒 Files selected for processing (2)

• changelog.d/7479-plan-step7-json.md
• docs/engine-plan.md

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📝 Walkthrough

Walkthrough

The engine plan now uses measured performance findings to sequence JSON-related work. The changelog records the updated plan, including DirectParser correctness work, tape materialization, validation requirements, and rejected optimization approaches.

Changes

Performance plan

Layer / File(s)	Summary
Measured backlog and sequencing docs/engine-plan.md, changelog.d/7479-plan-step7-json.md	The plan replaces the benchmark warning with measured backlog items, preserves the JSON roundtrip result, sequences DirectParser correctness before tape materialization work, and records checksum and quiet-host measurement requirements. The changelog documents the same sequencing and findings.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• PerryTS/perry#7285: Provides the public-baseline benchmark regeneration and JSON results used by this backlog.
• PerryTS/perry#7476: Provides refreshed JSON and polyglot benchmark findings incorporated into the plan.
• PerryTS/perry#7293: Earlier changes to the performance-planning content in docs/engine-plan.md precede this sequencing update.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/plan-step7-json-workstream

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