fix(server): detach immortal parent spans from idle background work

[lnieuwenhuis]

Long-lived parked fibers and the PortDiscovery poll loop retain their caller's parent span, even when a replacement span hides it from service lookup.

Fork through forkScopedDetached, which creates a fresh external parent and flattens the entire context before the child is created. Both activation paths and the port poller use it, preserving other services, the activation barrier, and scoped interruption. Idle ticks and secret reads avoid unnecessary spans.

Regression tests inspect retained context references in both activation paths and before child execution, and cover parent restoration and scoped interruption. The focused activation and port scanner suites pass (28 tests).

Related to #5410 and supersedes the approach in #5411. Removing this retained reference does not establish that Windows idle Private Bytes growth is resolved; a comparable long-running idle-memory measurement is still needed.

Originally built with muse-spark-1.3-contributor via OpenCode in T3 Code; retention fix implemented with GPT-6 via Codex.

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Note

Medium Risk
Changes tracing context for all forkParked background fibers and the preview port poll loop; behavior is intentional but affects observability and any code assuming inherited trace parents.

Overview
Long-lived server fibers (parked roots via forkParked, and the PortDiscovery poll loop) no longer inherit the ambient ParentSpan, which was pinning ever-growing trace state while the process idled.

A new withDetachedSpan re-roots work under a fresh stateless external span (typed so ParentSpan is satisfied without inheriting the caller’s span). forkParked always forks through that helper, so reactors like checkpoint/provider command processing get the same behavior.

PortScanner splits idle vs active poll ticks: the retain-count check runs outside Effect.fn, so idle ticks emit no PortDiscovery.pollTick spans under an ambient parent; active work still uses the named span. The repeating poll fiber is wrapped in withDetachedSpan, and the layer make span was removed.

ServerSecretStore.get drops its span in favor of Effect.withTracerEnabled(false) on reads. Tests cover re-rooting, forkParked non-inheritance, and idle poll span behavior.

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Note

Detach background fork and idle poll spans from ambient ParentSpan

• Adds withDetachedSpan in serverActivation.ts, which creates a fresh sampled external span and provides it as Tracer.ParentSpan for the wrapped effect
• Applies withDetachedSpan in forkParked so both activation-gated and ungated background forks run under a fresh root span instead of inheriting the caller's span
• Reworks PortDiscovery polling in PortScanner.ts: the repeating poll runs under a detached span, the PortDiscovery.make wrapper span is removed, and idle ticks return before the instrumented pollTickActive body so they no longer emit PortDiscovery.pollTick spans
• Disables tracing for the secret read wrapper in ServerSecretStore.ts, removing the ServerSecretStore.get span
• Risk: withDetachedSpan removes Tracer.ParentSpan from the required environment of wrapped effects; any caller that explicitly provides or depends on the ambient ParentSpan for forked work will now observe a different root span. The gated forkParked path preserves the same detached root across the activation release boundary.

^{Macroscope summarized c092eac.}

Summary by CodeRabbit

• Observability
  • Background operations now use independent tracing contexts for more accurate diagnostics.
  • Idle port-scanning polls no longer generate unnecessary tracing spans.
  • Server secret retrieval no longer produces a tracing span, reducing unrelated telemetry noise.
• Bug Fixes
  • Corrected tracing behavior for deferred activation and background processing so unrelated parent operations are not incorrectly associated.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The PR changes shared production background-task context and tracing behavior across multiple server workflows. It also modifies apps/server/src/auth/ServerSecretStore.ts, a sensitive authentication path, so the change warrants human review despite most additions being tests.

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[Benchance]

Linked from #5410. Please add Fixes #5410 to this PR description so the bug auto-closes on merge (#5411 is already closed as superseded by this).

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• apps/server/src/preview/PortScanner.ts
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📝 Walkthrough

Walkthrough

The changes detach background effects from ambient tracing, prevent spans for idle port polling, disable tracing for secret retrieval, and add tests for the updated behavior.

Changes

Tracing isolation and span suppression

Layer / File(s)	Summary
Detached tracing primitives apps/server/src/serverActivation.ts, apps/server/src/serverActivation.test.ts	forkScopedDetached forks effects with a flattened context and a fresh external parent span. forkParked uses it for immediate and deferred activation. Tests verify span isolation, context retention, and scope behavior.
Port polling span control apps/server/src/preview/PortScanner.ts, apps/server/src/preview/PortScanner.test.ts	Port polling separates the retain-count guard from active scanning. Repeated polling uses detached execution. Tests verify that idle ticks do not create PortDiscovery.pollTick spans.
Secret retrieval span suppression apps/server/src/auth/ServerSecretStore.ts	ServerSecretStore.get disables its named tracing span.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant forkParked
  participant forkScopedDetached
  participant FiberContext
  participant Tracer
  forkParked->>forkScopedDetached: fork activation effect
  forkScopedDetached->>FiberContext: flatten and replace context
  forkScopedDetached->>Tracer: create fresh external parent span
  forkScopedDetached->>forkParked: return scoped fiber

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Merge Risk: ⚪ Minimal · up to 30aa6

The tracing isolation and idle polling changes are covered by targeted tests, with no concrete merge-blocking risk identified.

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✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 5…
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Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main change: detaching parent spans from long-lived idle server work.
Description check	✅ Passed	The description clearly explains the changes, rationale, tests, risks, and known limitations. It does not use the template headings or checklist, but it contains the required substantive information a…

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Actionable comments posted: 1

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Inline comments:
In `@apps/server/src/serverActivation.ts`:
- Around line 49-51: Update the deferred activation sequence around
Deferred.succeed, activation, and detached so the entire wait-and-park flow
executes inside withDetachedSpan, ensuring the parked fiber does not retain the
ambient Tracer.ParentSpan while awaiting activation. Add a regression test that
inspects Tracer.ParentSpan before waiting on the activation gate.

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📒 Files selected for processing (5)

• apps/server/src/auth/ServerSecretStore.ts
• apps/server/src/preview/PortScanner.test.ts
• apps/server/src/preview/PortScanner.ts
• apps/server/src/serverActivation.test.ts
• apps/server/src/serverActivation.ts

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[shivamhwp]

Note: GPT-6 on behalf of shivam (@shivamhwp).

The background fiber still retains the original ParentSpan even though service lookup returns the external span. Effect's Context.add keeps the previous context in its overlay chain. Providing the replacement inside the child also keeps a restoration frame alive for the lifetime of the wrapped work. The original parent remains reachable until the background scope closes, including on the activation-gated path.

Detach before forking, and give the child a fresh flattened context with the replacement parent. Apply that to both forkParked branches and the PortDiscovery polling fork. Merely moving the current withDetachedSpan outside forkScoped still retains the parent through the context overlay. Preserve the other services, activation barrier, and scoped interruption.

Keep the description's limitation on #5410: removing this retained reference does not establish that Windows idle Private Bytes growth is resolved.

[lnieuwenhuis]

Addressed in 30aa6ef. The feedback matches Effect 4.0.0-rc.112: a replacement service can leave the old span in the context overlay/cache root, and providing it inside the child leaves a restoration frame alive.

forkScopedDetached now flattens the context into a fresh map and replaces it around forkScoped, before the child exists. Both forkParked branches and the PortDiscovery poller use that helper. Regression tests inspect retained references in both activation paths (both failed before the fix), check the child context before execution, and verify other services, caller parent restoration, the activation gate, and scoped interruption. All 28 focused activation/port-scanner tests, server typecheck, and targeted lint pass.

The description retains the #5410 limitation: this removes the demonstrated reference but does not prove Windows idle Private Bytes growth is resolved.