feat(rsc): bind accessed member expression value for use server closure

[hi-ogawa]

Description

• Closes server action closures should capture member access paths, not whole objects #1171
• Stacked on fix(rsc): handle shadowing for use server variable binding #1170

TODO

• review slop
• handle optional chain (maybe later)

[Copilot]

Pull request overview

This PR enhances the RSC server-action hoisting transform so closures that reference member-access chains (e.g. config.api.key) bind only the accessed subtree instead of serializing/binding the full root object. This reduces RSC payload size and avoids runtime serialization failures when the root contains non-serializable values.

Changes:

• Extend scope analysis to track the “outermost bindable” reference node per identifier (identifier vs. non-computed member-expression chain, with callee trimming).
• Update hoist binding to synthesize partial object literals per root identifier and bind those (while keeping the hoisted function parameter as the root name).
• Add/refresh fixtures + snapshots and add design notes; update formatter ignore patterns for new *.snap.js files.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/plugin-rsc/src/transforms/utils.ts	Adds a shared DefaultMap helper (moved out of tests).
packages/plugin-rsc/src/transforms/scope.ts	Tracks member-expression chains per reference (referenceToNode) and applies callee trimming.
packages/plugin-rsc/src/transforms/scope.test.ts	Updates scope serializer to optionally display the tracked reference node; uses shared DefaultMap.
packages/plugin-rsc/src/transforms/hoist.ts	Changes bind-var extraction to synthesize partial-object bind expressions for member chains.
packages/plugin-rsc/src/transforms/hoist.test.ts	Adds fixture-based snapshot testing for hoist output and updates/clarifies some existing edge-case comments.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain.js	New fixture for plain member chain reference-node tracking.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain.js.snap.json	Snapshot for plain member chain reference-node tracking.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-optional.js	New fixture for optional-chain boundary behavior.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-optional.js.snap.json	Snapshot for optional-chain boundary behavior.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-computed.js	New fixture for computed-access boundary behavior.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-computed.js.snap.json	Snapshot for computed-access boundary behavior.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-callee.js	New fixture for callee-trimming behavior.
packages/plugin-rsc/src/transforms/fixtures/scope/reference-node/member-chain-callee.js.snap.json	Snapshot for callee-trimming behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain.js	New hoist fixture for partial-object binding of member chains.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain.js.snap.js	Snapshot for member-chain partial-object binding.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-siblings.js	New hoist fixture for merging sibling paths under one root.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-siblings.js.snap.js	Snapshot for sibling-path merge binding.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-root.js	New hoist fixture where direct root access forces binding the whole root.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-root.js.snap.js	Snapshot for root-access override binding.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-optional.js	New hoist fixture for optional-chain conservative fallback behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-optional.js.snap.js	Snapshot for optional-chain fallback behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-dedupe.js	New hoist fixture for prefix dedupe behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-dedupe.js.snap.js	Snapshot for prefix-dedupe binding result.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-computed.js	New hoist fixture for computed-access conservative fallback behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-computed.js.snap.js	Snapshot for computed-access fallback behavior.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-callee.js	New hoist fixture verifying callee trimming preserves receiver capture.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-callee.js.snap.js	Snapshot for callee-trimming hoist output.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-unsupported.js	New hoist fixture covering multiple unsupported patterns.
packages/plugin-rsc/src/transforms/fixtures/hoist/member-chain-unsupported.js.snap.js	Snapshot for unsupported-pattern binding behavior.
packages/plugin-rsc/docs/notes/2026-04-05-rsc-member-chain-binding-plan.md	Design note documenting the chosen approach and rationale.
packages/plugin-rsc/docs/notes/2026-04-05-member-chain-optional-computed-follow-up.md	Follow-up note outlining optional/computed access support considerations.
.oxfmtrc.json	Expands ignore pattern to cover *.snap.* (including new *.snap.js).

Comments suppressed due to low confidence (1)

packages/plugin-rsc/src/transforms/scope.test.ts:10

• Typo in comment: “snaphsot” → “snapshot”.

// - use single markdown as snaphsot? (cf. review-scope-fixtures.ts)

describe('fixtures', () => {

---

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