Pin managed fetch dispatcher

[jesse-merhi]

Summary

• Pins managed globalThis.fetch calls to the active Proxyline dispatcher so later setGlobalDispatcher() calls cannot bypass managed proxy routing.
• Preserves invalid primitive fetch init rejection behavior while overriding explicit dispatcher options in managed mode.
• Updates README, docs, security notes, and changelog to distinguish global fetch coverage from imported Undici APIs.

Verification

• git diff --check
• fnm exec --using v22.21.0 pnpm check
• $code-review clean: Codex review clean plus cold/manual pass with no remaining actionable findings.

[Copilot]

Pull request overview

Pins the managed globalThis.fetch patch to Proxyline's own dispatcher by explicitly setting (rather than stripping) the dispatcher init field, so that a later setGlobalDispatcher() cannot bypass managed proxy routing. Also preserves Undici's primitive-init rejection behavior and updates docs/changelog to clarify global fetch coverage vs. imported Undici APIs.

Changes:

• Replaced stripFetchDispatcher with withManagedFetchDispatcher, which validates primitive init values and pins Proxyline's active managed dispatcher into the init.
• Added tests covering invalid primitive init rejection and proxy routing surviving a setGlobalDispatcher() replacement in managed mode.
• Updated README, surfaces.md, security.md, and CHANGELOG to describe the pinned-dispatcher behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/runtime.ts	Refactor fetch init handling to pin managed dispatcher and validate primitive init.
test/package.test.ts	New test verifying primitive init values are rejected with a TypeError.
test/e2e.test.ts	New e2e test confirming managed routing survives setGlobalDispatcher.
README.md	Clarify global fetch vs. Undici global dispatcher coverage.
docs/surfaces.md	Update managed fetch description to reflect pinned dispatcher.
docs/security.md	Update out-of-scope and threat table entries for pinned dispatcher.
docs/README.md	Mirror README clarification on fetch coverage.
CHANGELOG.md	Add 0.3.3 entry for the fix.

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[steipete]

Thanks @jesse-merhi. This landed in 5d3dc51, with follow-up changelog credit in b7f22d5 because the PR branch could not be updated from this checkout.