Preserve snapshot identity across no-op updates

[Andrew Branch (andrewbranch)]

Missed this in #64204

[Copilot]

Copilot review overview

🟡 Changes recommended

Same-ID updates leak the additional server-side snapshot reference.

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Review effort: Balanced
Findings: 2

Open (2)

• Release server reference before no-op update return · New
• Balance duplicate snapshot reference on no-op update · New

What changed in this PR

Preserves client snapshot identity when no-op updates return the existing snapshot ID.

Changes:

• Reuses the base snapshot for matching IDs.
• Adds sync and async identity tests.

File	Description
packages/​typescript/​src/​api/​sync/​api.ts	Reuses snapshots in sync and generator paths.
packages/​typescript/​src/​api/​async/​api.ts	Reuses snapshots in the async path.
packages/​typescript/​test/​sync/​api.test.ts	Tests sync identity preservation.
packages/​typescript/​test/​async/​api.test.ts	Tests async identity preservation.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Same-ID responses can contain request-specific operation results that are currently discarded.

Review effort: Balanced
Findings: None

Resolved since last review (2)

• Balance duplicate snapshot reference on no-op update
• Release server reference before no-op update return

Previously missed (2)

In code that hasn't changed since last review

Retain openedFiles results for state-level no-op updates

packages/​typescript/​src/​api/​async/​api.ts:413

Returning baseSnapshot discards the operation results associated with this update request. A state-level no-op can still have openedFiles results, so callers may receive the base object's stale operation and even a runtime tuple shape that contradicts this overload's inferred type. Preserve identity only when both response operation fields are absent.

Preserve operation results when reusing snapshot IDs

packages/​typescript/​src/​api/​sync/​api.ts:645

Returning baseSnapshot here discards data.operation, although operation results are correlated with the current request. A no-state-change request can still carry results (for example, repeated/subset openFiles, including an empty tuple), so this can return stale results from the base request and violate the inferred tuple type. Reuse identity only when the response has no operation fields; otherwise construct the new wrapper for this server snapshot ID.

This issue also appears on line 673 of the same file.