Fix stableStringify treating shared references as circular

[Dmitry Savy (dsavy4)]

_stableStringify guards against circular references with a WeakSet, but it never removes a value from the set after serializing its subtree. So a value that is shared across sibling branches, which is a DAG and not a cycle, gets reported as "[Circular]" on every occurrence after the first.

Repro:

const shared = { a: 1 };
stableStringify({ x: shared, y: shared });
// before: {"x":{"a":1},"y":"[Circular]"}
// after:  {"x":{"a":1},"y":{"a":1}}

This matters because stableStringify is used to compare objects for change detection (for example in the chat voice client, stableStringify(current[key]) !== stableStringify(prev[key])), where a shared reference can make two structurally equal objects compare as different.

The fix tracks only the current ancestor path by removing the value from the set once its subtree is done, so true cycles are still detected while shared references serialize in full. Added tests for shared references in both object and array positions, and the existing circular-reference test still passes.

[Copilot]

Pull request overview

Fixes stableStringify to distinguish shared references from circular references.

Changes:

• Tracks only the active ancestor path during serialization.
• Adds object and array shared-reference regression tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/vs/base/common/objects.ts	Removes serialized values from cycle tracking.
src/vs/base/test/common/objects.test.ts	Tests repeated shared references.

[Dmitry Savy (dsavy4)]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Connor Peet (connor4312)]

thanks!