fix(extension-mgmt): record concurrent install result so callers don't see "Unknown error"

[bryanchen-d]

Summary

Fixes a race in installFromGallery that surfaces in telemetry as Unknown error while installing extension <id> for ~1,484 unique users in the last 14 days (bucket 810ac6ce…, github.copilot-chat), plus three other extension-specific buckets.

Linked issues: #310858 (open, currently auto-triaged with the same root-cause analysis), #293368 (closed for "not enough information" — this PR explains the missing piece).

Root cause

AbstractExtensionManagementService.installExtensions(...) keeps a class-level map installingExtensions of in-flight installs keyed by (extensionId, profileLocation). When a second installFromGallery(extA) arrives while a first is still running, the top-level loop takes the "wait for existing task" branch:

const existingInstallExtensionTask = ...this.installingExtensions.get(...);
if (existingInstallExtensionTask) {
    alreadyRequestedInstallations.push(existingInstallExtensionTask.task.waitUntilTaskIsFinished());
} else {
    createInstallExtensionTask(...);
}

Only createInstallExtensionTask populates the local installingExtensionsMap, so the parallel-install loop and the deps loop both iterate over an empty map and nothing writes into installExtensionResultsMap.

After the awaited tasks complete, the function does:

if (alreadyRequestedInstallations.length) {
    await this.joinAllSettled(alreadyRequestedInstallations);   // result discarded
}
...
return [...installExtensionResultsMap.values()];                // → []

Back in installFromGallery:

const results = await this.installGalleryExtensions([{ extension, options }]);
const result = results.find(...);                       // undefined
if (result?.local)  return result.local;                // miss
if (result?.error)  throw result.error;                 // miss
const redirectedResult = results[0];                    // undefined
if (redirectedResult?.local) return redirectedResult.local;     // miss
if (redirectedResult?.error) throw redirectedResult.error;      // miss
throw new ExtensionManagementError(`Unknown error while installing extension ${extension.identifier.id}`, ExtensionManagementErrorCode.Unknown);

Two failure modes, one symptom:

• In-flight install succeeded → caller throws "Unknown error" even though the extension is installed.
• In-flight install failed → joinAllSettled rethrows; the outer catch only iterates the (empty) installingExtensionsMap so no real error is recorded; control falls through and return [] → caller throws the generic message instead of the underlying cause. (This is why [Unhandled Error] Unknown error while installing extension github.copilot-chat #293368 had no actionable info.)

Fix

When the existing-task branch is taken, attach .then(...) / .catch(...) to waitUntilTaskIsFinished() and write the resolved ILocalExtension (or rejection reason, normalized via toExtensionManagementError) into installExtensionResultsMap keyed identically to primary tasks (${identifier.id.toLowerCase()}-${profileLocation.toString()}). On the failure path we still re-throw so the existing joinAllSettled rejection / outer catch semantics are preserved.

After the fix:

• Concurrent install succeeded → installFromGallery's results.find(...) returns the real ILocalExtension. ✅
• Concurrent install failed → installFromGallery throws the real error (e.g. network / signature / disk-full), which is what sandy081 needs to investigate. ✅

No public API changes. ~28 lines net.

Telemetry context

Bucket	Extension	Hits / 14d	Users / 14d	Versions
810ac6ce…	github.copilot-chat	3,525	1,484	1.116, 1.117
33a063ed…	anthropic.claude-code	432	144	1.116–1.118.1
fad68ea2…	ms-ceintl.vscode-language-pack-zh-hans	240	144	1.116–1.118.1
09e28363…	ms-python.python	385	121	1.116–1.118.1

All four buckets share the exact stack frame at abstractExtensionManagementService.ts:184 (the throw new ExtensionManagementError("Unknown error...") line).

[Copilot]

Pull request overview

This PR fixes a race in AbstractExtensionManagementService.installExtensions(...) where concurrent installFromGallery calls could return an empty results array, causing callers to throw a generic Unknown error while installing extension <id> even when the underlying in-flight install actually succeeded or failed with a real error. The change ensures that when an install is already in progress, the waiting caller still records the resolved ILocalExtension or the normalized error into installExtensionResultsMap, allowing installFromGallery to surface the correct outcome.

Changes:

• When this.installingExtensions already contains an in-flight task, attach handlers to waitUntilTaskIsFinished() and populate installExtensionResultsMap for that caller.
• Preserve existing rejection behavior by rethrowing after recording the error, so joinAllSettled semantics remain unchanged.

Show a summary per file

File	Description
src/vs/platform/extensionManagement/common/abstractExtensionManagementService.ts	Records results for “already in-flight” installs so concurrent callers don’t fall back to the generic “Unknown error” path.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 2