fix(vscode): a more compact serializer outcome

[WebReflection]

What Problem This Solves

The tuple serializer introduced in #13733 repeats full JavaScript type names and array wrappers for every scalar, making Agent Manager’s internal change-detection keys unnecessarily long.

Why This Change Was Made

Use compact numeric type IDs and id:payload string leaves while retaining the original recursive mapping, scalar conversion, negative-zero handling, and JSON escaping. This follows the compact-serializer discussion on #13733 without changing which supported, ordinary acyclic inputs produce equal keys.

User Impact

Reduce internal PR-signature and filesystem-stamp key sizes without changing update detection or requiring stored-state migration. There is no visible UI change.

Evidence

The tuple [0, -0, 0n, [1, 2, 3]] shrinks from 94 to 40 characters and UTF-8 bytes, approximately 57%. Every scalar occurrence saves 9–12 characters and bytes; arrays and holes add no new overhead, so array/hole-only inputs remain unchanged rather than becoming larger. Regression coverage checks scalar distinctions, exact bigints, signed zero/nonfinite numbers, escaped text, nesting, sparse holes, and structural equality across separate allocations.

A before/after differential run using Bun 1.3.14 compared 596 cases, including a deterministic 546-entry sparse-tuple corpus, against keys captured from the original export. Both directions preserved all 397 equality groups: 547 cases became shorter and 49 stayed byte-for-byte identical.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• .changeset/compact-vscode-serializer.md
• packages/kilo-vscode/src/util/serialize.ts
• packages/kilo-vscode/tests/unit/serialize.test.ts

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_{Review guidance: REVIEW.md from base branch main}