refactor(codegen): delete codegen.mjs; outer agent owns script generation

[ziruihao]

Summary

PR #125 introduced scripts/codegen.mjs as a one-shot completion-API pipeline that templates a framework prompt, calls the LLM, writes the emitted message text as the script, verifies, and rewrites on failure. The sub-process boundary turned out to be the wrong contract.

Every bug we shipped fixes for since #125 merged was caused by it:

bug	wouldn't exist if outer agent owned codegen
LLM preamble bleeds into .ts file	Write({content}) is a structured argument — script bytes never ride the natural-language channel
Shared --out dir package.json collision (70dae51)	One agent writes one package.json, deduped at source
pkg-hash install-stamp gate (55e7d4c)	Agent re-installs when it knows deps changed
Cross-runner PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD leak	Agent sets env when it spawns verify
Parent verify timeout < child runner timeout (8638b7e)	One process, no nested timeouts
Stagehand script vanishing pre-upload	The agent that decides "stagehand failed" is the same one curling the upload

Verified end-to-end against the 2026-06-04 preview run: 4 of 5 browser/hybrid skills lost their stagehand.ts because the LLM's rewrite output prepended a paragraph of self-narration before the imports. Cache file at /tmp/skill/etsy.com/search-products/autobrowse/codegen-cache/6c78b599d4d5a9d4.txt:

"The error is clear: the previous attempt's output started with explanation text ("Looking at the error...") before the imports, which caused esbuild to fail parsing. The script content must start directly with imports. Here is the complete corrected script:"

…followed by valid imports. tsx chokes on the prose, verify fails, retry loop never converges. The earlier draft of this PR added a stripPreamble defensive boundary; this version removes the boundary problem entirely.

What changes

• Delete scripts/codegen.mjs (515 lines)
• Delete codegen/runners/ (tsx-runner.mjs, playwright.mjs, stagehand.mjs)
• Delete codegen/scaffolds/ — inlined into the new reference docs
• Move + reframe codegen/prompts/{playwright,stagehand}.md → references/codegen/{playwright,stagehand}.md. Technical content (CDP-attach pattern, Stagehand v3 constructor shape, locator priorities, snap convention, JSON stdout contract) is preserved; framing shifts from "you ARE this LLM emitting verbatim" to "here's the spec for the file you're writing".
• Update SKILL.md's "Generate a runnable script" section to describe the agent-driven loop (Read trace/refs → Write script → Bash verify → iterate or delete on persistent failure).

Net diff: −626 lines.

Companion change

The browse.sh §4b rewrite — replacing the node codegen.mjs --frameworks ... invocation with the inlined Read/Write/Bash loop — ships in a separate browse.sh PR (to follow).

Test plan

• No external callers in this repo reference the deleted paths
• Companion browse.sh PR opens
• After both land + BB_SKILLS_SHA bumps on the preview, re-regenerate the 5 stagehand-missing skills (etsy, google-search-flights, nursys, amazon-search-products, uspto-search-patents) and confirm both playwright.ts and stagehand.ts upload

🤖 Generated with Claude Code

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Note

Medium Risk
Large removal of the codegen/verify harness shifts behavior to agent-driven steps; any caller still invoking codegen.mjs or npm run codegen will break until updated (e.g. browse.sh companion PR).

Overview
Removes the standalone codegen pipeline (scripts/codegen.mjs plus runners, scaffolds, and LLM prompt templates) and moves script generation to the outer agent via Read / Write / Bash as documented in SKILL.md.

The old node codegen.mjs flow (cached Anthropic completion, scaffold drop, nested verify runners) is replaced by an explicit loop: read converged trace + strategy.md + references/codegen/<framework>.md, write playwright.ts / stagehand.ts and merged scaffolds, run npm install + npx tsx against a fresh Browserbase session, iterate on stderr or delete broken scripts before upload.

Playwright and Stagehand specs are reframed from “system prompts for a sub-process LLM” to references/codegen/playwright.md and stagehand.md, with inlined package.json / tsconfig guidance (including HTTP-only Playwright, Stagehand skip rules, and shared-dir package.json merge). Net effect is a large deletion (~600+ lines) with workflow ownership shifted to the skill agent; browse.sh’s codegen.mjs invocation is expected to follow in a companion PR.

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