fix(server): editors appear once a slow discovery scan finishes

[bfowler]

Follow-up to #13669, continues fixing #4697. On a busy host (for example right after an update restarts the server alongside hundreds of git status checks), editor discovery can still outlast server.getConfig's five-second bound. Server traces from an affected machine show one connect cut off at 5.009s and getting [], and a second connect 20 seconds later finishing in 3.5s. The window that got [] never recovered: the timeout cancelled its scan so nothing was cached, and availableEditors only travels in the one-time config snapshot.

Fix

• Discovery outlives its callers. The launcher runs each scan on its own fiber in the service scope, and every caller awaits that one scan. A connect that times out or disconnects stops waiting, but the scan finishes and is cached, so concurrent connects share one scan instead of each starting their own. A failed scan clears the entry so the next caller starts over.
• Late editors reach the client. When the scan finishes after a subscriber's snapshot went out without it (or without the file manager's reveal kind), subscribeServerConfig sends a fresh snapshot. Clients already replace their config on any snapshot, so there is no contract or client change. The resent config is folded from the live updates the stream has already sent rather than reloaded, so a settings, provider, or keybindings change that landed meanwhile is never rolled back. The reveal-kind probe is not shared like the scan, so the recovery runs it without the snapshot's timeout; otherwise a probe that always takes longer would be cancelled every time.

Tests

• Launcher: an interrupted caller no longer cancels the scan, and the next caller joins it (fails on the old launcher).
• Config stream (withLateEditorConfig, ws.test.ts): late editors are resent without rolling back a settings change delivered while the scan ran; a late file manager reveal kind is resent; a scan that matches the snapshot sends nothing.
• With the real launcher: the scan parks past the five-second timeout, the snapshot gets no editors, and the late snapshot has them.
• With the real launcher: a reveal-kind probe that runs past five seconds still lands in the late snapshot.

Not addressed here: each command lookup still re-stats every PATH directory to check its mtime, which is most of the ~1,500 filesystem calls on a 75-entry PATH. That now only delays the list rather than emptying it.

Model: Claude Opus 5.5 (1M context). Harness: Claude Code in T3 Code.

[macroscopeapp]

🟡 Medium process/externalLauncher.ts:808

A discovery scan that never completes permanently blocks resolveAvailableEditors(): every later caller reuses the same unfinished Deferred and no replacement scan can start until restart. This happens because the pending entry stores expiresAtNanos: undefined and is cleared only by the scan's onExit; give pending scans a finite expiry so callers can start a replacement after the cache TTL.

Suggested change

	return [[scan, true], Option.some({ scan, expiresAtNanos: undefined })];
	return [[scan, true], Option.some({ scan, expiresAtNanos: nowNanos + EDITOR_DISCOVERY_CACHE_TTL_NANOS })];

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In file @apps/server/src/process/externalLauncher.ts around line 808:

A discovery scan that never completes permanently blocks `resolveAvailableEditors()`: every later caller reuses the same unfinished `Deferred` and no replacement scan can start until restart. This happens because the pending entry stores `expiresAtNanos: undefined` and is cleared only by the scan's `onExit`; give pending scans a finite expiry so callers can start a replacement after the cache TTL.

[bfowler]

Not changing this. A scan that never settles can't block anything unboundedly: its only callers are server.getConfig/the config snapshot, which still bound it with the 5 s resolveAvailableEditorsForConfig timeout and degrade to no editors (the pre-PR behavior), and the late-snapshot wait, which ends with its subscription.

The suggested expiry would make things worse in the one case where a scan really hangs: a stat stuck on a dead network mount or PATH entry. A replacement scan every 60 s would hit the same entry and hang too, and each stuck fs.stat holds a libuv threadpool thread (4 by default), so piling up scans would starve every other filesystem call on the server. Keeping at most one scan in flight is deliberate. It also races with in-flight scans that take longer than the TTL, starting duplicates on a slow host, which is the situation this PR is about.

[macroscopeapp]

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[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a targeted fix for slow editor discovery, but it introduces shared background fibers and late WebSocket configuration snapshots with nontrivial timeout, lifecycle, and event-ordering behavior. Human review is warranted for those production-side effects, with unresolved medium-severity findings also requiring attention.

Not approved because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

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📝 Walkthrough

Walkthrough

Editor discovery now shares in-progress scans across callers and caches successful results for 60 seconds. Server config subscriptions can publish a later snapshot with discovered editor capabilities while preserving intervening config updates.

Changes

Editor discovery and server config

Layer / File(s)	Summary
Shared editor scan and retry apps/server/src/process/externalLauncher.ts, apps/server/src/process/externalLauncher.test.ts	Discovery callers reuse in-progress scans. Successful results are cached for 60 seconds, and failed scans clear the cache entry. The test verifies that interrupting one caller does not start a second scan.
Editor config snapshots apps/server/src/ws.ts, apps/server/src/ws.test.ts	Config loading resolves editor and file-manager reveal fields. Subscriptions can emit a later editor snapshot while retaining intervening settings, keybinding, and provider updates. Tests cover delayed discovery and snapshot differences.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant subscribeServerConfig
  participant withLateEditorConfig
  participant EditorDiscovery
  participant ConfigStream
  subscribeServerConfig->>withLateEditorConfig: wrap live updates
  withLateEditorConfig->>EditorDiscovery: discover editor capabilities
  EditorDiscovery-->>withLateEditorConfig: return editor config
  withLateEditorConfig->>ConfigStream: emit updated snapshot

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Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to e6298

The late editor update can remain in the configuration subscription. No confirmed issue remains that needs fixing before merge.

Security Architecture Review

Security architecture risk: 🔵 Low · up to e6298

The changed discovery path remains behind authentication and preserves newer configuration updates when publishing late editor capabilities. No new privilege or data-exposure path was demonstrated. Recovery from indefinitely blocked discovery and failure during lifecycle transitions remains less fully validated.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — A pending or failed shared scan affects capability discovery for callers using the same launcher instance. Published results describe that host's known editors and file-manager capability; the inspected change does not establish cross-environment access or increased process privileges.

Security Findings and Attack Paths

• inferred — No introduced attacker-selected command path was demonstrated in the changed discovery flow. An authenticated client can trigger configuration discovery, but the scan reads host environment information and iterates fixed editor definitions; the resulting snapshot carries capability metadata rather than launch authority.

Trust Boundaries and Controls

• observed — Late snapshots remain within the authenticated configuration subscription. They reuse current stream state, including settings already passed through client redaction, rather than rereading and republishing an older settings snapshot.

Resilience and Maintainability Implications

• observed — The initial config wait retains its five-second fallback, and the Linux directory-handler subprocess probe has its own two-second timeout. The shared scan has no independent overall deadline or in-progress expiry, so a blocked filesystem probe can keep discovery pending until completion or service-scope interruption. Expected probe errors are converted to unavailable results; unexpected defects remain a possible stream-termination path.

Hardening Proposals

• proposed — Consider a separate, longer service-owned discovery deadline or stuck-scan recovery policy that preserves independence from caller timeouts while completing waiters and allowing subsequent retries.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: editors become available after a slow discovery scan finishes.
Description check	✅ Passed	The description explains the problem and fix, and lists focused tests. It does not include the template’s Scope and approval section or state the observed test results, but the core description is mos…

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Inline comments:
In @apps/server/src/ws.ts:
- Around line 3719-3725: Update lateEditorConfig to call resolveEditorConfig
before filtering, then emit the result when either availableEditors or
shellRevealInFileManagerKind differs from config; this lets unchanged editor
lists still trigger a fresh reveal-kind update.

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[macroscopeapp]

🟡 Medium src/ws.ts:3773

An opted-in subscribeServerConfig client loses its recently received environment themes or usage-limit sources when editorsResolved arrives. mapAccum forwards those events but leaves current unchanged, so the later snapshot is rebuilt from the original config without those fields; fold both update types into current before emitting the snapshot.

+                        case "environmentThemesUpdated":
+                          return [{ ...current, environmentThemes: event.payload.themes }, [event]];
+                        case "usageLimitSourcesUpdated":
+                          return [{ ...current, usageLimitSources: event.payload.sources }, [event]];
                         case "keybindingsUpdated":

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In file @apps/server/src/ws.ts around line 3773:

An opted-in `subscribeServerConfig` client loses its recently received environment themes or usage-limit sources when `editorsResolved` arrives. `mapAccum` forwards those events but leaves `current` unchanged, so the later snapshot is rebuilt from the original config without those fields; fold both update types into `current` before emitting the snapshot.

[bfowler]

Not changing this. Themes and usage-limit sources are never part of a config snapshot by contract (ServerConfig.environmentThemes / usageLimitSources docs in packages/contracts/src/server.ts): their streams replay the current set on subscribe, so putting them in the snapshot too would send every subscriber the same arrays twice.

The client is built around that. applyServerConfigProjection (packages/client-runtime/src/state/serverConfigProjection.ts) carries the previously projected themes and sources across any snapshot whose environment.capabilities advertise them, and the late snapshot keeps environment from the folded config, so those capabilities stay set. A late editorsResolved snapshot therefore can't drop either field on the client.

Folding them into the snapshot as suggested would break that contract and resend the arrays on the wire. Passing those events through without recording them is intentional.

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[Yash-Singh1]

Oops, I missed this. LGTM after conflicts are resolved.

[bfowler]

@Yash-Singh1 thanks! Conflicts are resolved and CI is green on 185f970. Two changes since your approval, in case you want to look again:

• The orchestrator rewrite (feat(orchestrator): introduce new orchestrator #2829) removed server.test.ts and its WebSocket harness. The late-resend logic now lives in an exported withLateEditorConfig in ws.ts, and its tests moved to ws.test.ts. Behavior is unchanged.
• 185f970: the background recovery no longer puts the five-second timeout on the reveal-kind probe. That probe isn't shared like the editor scan, so one that always ran longer was cancelled every time. The snapshot is still bounded. A real-launcher test covers it.