feat: integrate Partytown with first-party proxy mode

[harlan-zw]

❓ Type of change

• 📖 Documentation
• 🐞 Bug fix
• 👌 Enhancement
• ✨ New feature
• 🧹 Chore
• ⚠️ Breaking change

📚 Description

Partytown and first-party proxy mode were completely separate code paths — Partytown scripts bypassed bundling/URL rewriting, and the intercept plugin (main-thread monkey-patches) couldn't reach Partytown's web worker. This meant scripts loaded from third-party domains and all tracking requests went unproxied.

This PR integrates the two via three points:

1. resolveUrl generation — generates a Partytown resolveUrl function from the same intercept rules used by the main-thread intercept plugin. This is the web-worker equivalent — Partytown calls it for every network request (fetch, XHR, sendBeacon, Image) made by worker-executed scripts.

2. skipApiRewrites for partytown scripts — when bundling scripts for Partytown, URL string literals are still rewritten but API call rewrites (fetch → __nuxtScripts.fetch, etc.) are skipped since __nuxtScripts doesn't exist in the worker context and resolveUrl handles interception instead.

3. Auto-configuration — after finalizeFirstParty, auto-configures @nuxtjs/partytown's resolveUrl from the computed intercept rules. Warns if user already has a custom resolveUrl.

Flow for a partytown + first-party script

1. Build: Script downloaded, URLs rewritten via AST (API calls left alone), served as bundled asset
2. SSR: useScript partytown quick-path renders <script src="/_scripts/assets/bundled.js" type="text/partytown"> (src already rewritten by transform)
3. Worker: Partytown loads bundled script in worker. Static URLs already point to proxy. Dynamic URLs caught by resolveUrl → rewritten to /_scripts/p/*
4. Server: Nitro proxy handler forwards to third-party with privacy transforms

Changed files

File	Change
src/first-party/partytown-resolve.ts	New — generatePartytownResolveUrl()
src/first-party/setup.ts	finalizeFirstParty returns interceptRules alongside devtools data
src/first-party/index.ts	Re-exports new function and type
src/module.ts	Auto-configures partytown resolveUrl, passes partytownScripts to transform
src/plugins/rewrite-ast.ts	skipApiRewrites option on rewriteScriptUrlsAST
src/plugins/transform.ts	Accepts partytownScripts set, passes skipApiRewrites for partytown scripts
test/unit/rewrite-ast.test.ts	Tests for skipApiRewrites + generatePartytownResolveUrl

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Project	Deployment	Actions	Updated (UTC)
scripts-playground	Building	Preview, Comment	Mar 19, 2026 11:13am

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commit: 0cb02d3

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 86f4f42e-f22c-4f0b-989e-b255d511a95c

📥 Commits

Reviewing files that changed from the base of the PR and between d25917e and 0cb02d3.

📒 Files selected for processing (7)

• src/first-party/index.ts
• src/first-party/partytown-resolve.ts
• src/first-party/setup.ts
• src/module.ts
• src/plugins/rewrite-ast.ts
• src/plugins/transform.ts
• test/unit/rewrite-ast.test.ts

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📝 Walkthrough

Walkthrough

This pull request introduces Partytown integration support by adding a URL resolver generation mechanism and restructuring first-party configuration return values. A new generatePartytownResolveUrl function creates JavaScript code that resolves intercepted requests to first-party proxy paths based on configured rules. The finalizeFirstParty function now returns a structured FinalizeFirstPartyResult containing intercept rules and optional devtools data. The module automatically configures Partytown's resolveUrl when Partytown is enabled and intercept rules are available. AST rewriting logic is extended to conditionally skip API call rewrites for Partytown-managed scripts. Tests validate both the new resolve URL generator and conditional AST rewriting behavior.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~30 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main feature: integrating Partytown with first-party proxy mode, which aligns with all changes in the PR.
Description check	✅ Passed	The description includes the type of change (New feature), detailed explanation of the problem and solution, and comprehensive documentation of the integration flow and changed files.

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• Commit unit tests in branch feat/partytown-first-party

📝 Coding Plan

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