NES: cache cross-file suggestions under the active document

[ulugbekna]

What

Extends Next Edit Suggestion (NES) caching to support cross-file suggestions — a suggestion the model returns for a document other than the one being edited.

Previously a cross-file suggestion was cached only under the target document's content (B(content) → edit), so it could only be re-served from cache after the user navigated to B. This change additionally caches it under the active document:

A(content + edit window) → edit-in-B

so the cross-file suggestion can be re-served from cache while the cursor is still in A — the same place it was produced.

How

• Cache (nextEditCache.ts) — CachedEdit/CachedEditOpts gain targetDocId? (the document the edit applies to, when different from the key document) and targetDocumentBeforeEdit? (a snapshot of that document's content the edit's offsets index into). The cursor-distance rejection is skipped for cross-file entries (their edit is in the target's coordinate space), while edit-window gating — which is in the active document's coordinates — is kept.

• Provider write path (nextEditProvider.ts) — when the first streamed edit targets a different document, a small helper also stores the A‑keyed cross-file entry (exact content match only, never rebased). At stream end the active document is no longer cached as "no edit" when a cross-file entry was just stored under the same key, which would otherwise clobber it. Applied to both the normal and speculative paths.

• Provider read path (nextEditProvider.ts) — a cross-file cache hit is served only while its target document is open and byte-identical to the stored snapshot. Otherwise the hit is treated as a cache miss → fresh fetch, rather than serving a misplaced edit or getting stuck re-serving a dead entry until the active document changes.

This is always on (no config flag).

Two invalidation layers

1. Default config — editing the target document already purges cross-document cache entries (the existing InlineEditsTriggerOnEditorChangeAfterSeconds purge, default 10).
2. Read-path validity guard — additionally covers the closed-target case (closing isn't an edit, so no purge) and the purge-disabled configuration.

Tests

7 cross-file tests in nextEditProviderCaching.spec.ts, assertions are behavioral (served edit + provider call-count, deterministically waiting for the first request's stream-end before re-requesting):

• re-serves on a 2nd trigger in A and survives the no-suggestions stream-end (no clobber);
• re-serves within / refetches outside the cached edit window;
• refetches when the target document is closed;
• control: with the purge disabled and the target unchanged, re-serves from cache (isolates the guard);
• refetches when the target changed — once with the purge disabled (guard fires) and once under the default config (purge fires).

Validation

• nextEditProviderCaching.spec.ts: 11/11 pass; broader NES suite: 89 pass / 2 pre-existing skips.
• Typecheck (tsgo --noEmit) and eslint clean on all changed files.

Out of scope

• Rebasing the active-document-keyed entry across edits in the active document (exact-match only).
• Hardening the fresh cross-file path against the target changing in-flight (pre-existing; subsequent re-serves are already protected by the new guard).

[Copilot]

Pull request overview

This PR extends Next Edit Suggestion (NES) caching to better support cross-file suggestions by additionally caching cross-file edits under the active document key, and adding a read-path validity guard to ensure cross-file cache hits are only served when the target document is open and byte-identical to the stored snapshot.

Changes:

• Extend cache entry metadata (targetDocId, targetDocumentBeforeEdit) to represent cross-file edits and safely validate them at read time.
• Update NextEditProvider to (a) cache cross-file edits under the active document key, and (b) avoid clobbering that entry with a “no suggestions” cache write at stream end.
• Add a dedicated cross-file caching test suite covering cache re-serve, edit-window gating, closed-target behavior, and stale-target invalidation paths.

Show a summary per file

File	Description
extensions/copilot/src/extension/inlineEdits/test/node/nextEditProviderCaching.spec.ts	Adds cross-file caching scenarios and assertions for re-serve vs refetch behavior.
extensions/copilot/src/extension/inlineEdits/node/nextEditProvider.ts	Implements active-document-keyed caching for cross-file edits plus read-path validity checks and stream-end clobber avoidance.
extensions/copilot/src/extension/inlineEdits/node/nextEditCache.ts	Extends cached edit metadata to carry cross-file target info and adjusts cursor-distance rejection behavior for cross-file entries.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Low