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perf(server): avoid repeated timeouts on linked-environment calls - #26551
When a linked environment's first configured address stops responding but an alternate works, every forwarded RPC repeats the first address's full descriptor timeout. PeerLinks.resolve starts at the first configured URL on every call, even immediately after verifying a working fallback.
Change
Prefer a verified fallback for a fixed 60 seconds after verification completes. Reuse does not extend the window. Expiry retries configured order; primary recovery, relinking and unlinking clear the preference. Starting the window after verification matters when several failed probes take a long time.
The map is allocated only after fallback use and capped at 256 entries containing a URL, credential-generation identifier and deadline. Every call still reads the link and credential, checks link expiry, and freshly checks peer identity and linked-agent limit capabilities. Healthy primary calls add no preference entry.
Tradeoff: a recovered preferred direct route can wait up to 60 seconds while the working fallback is used. The shared server resolver serves all clients/providers/MCP callers; no client UI, wire contract or provider adapter changes. Listing keeps its existing route order.
Scope and approval
Submitted under the small, focused obvious-defect exception: repeated full failed-route timeouts despite a freshly verified working alternate are the single defect addressed. This proposes that exception honestly; it does not claim maintainer approval or a triage exemption.
Open #26475 changes Tailscale address trust in the same resolver and needs coordination if both land. #24849 changes client socket stability; #26169 changes client route ranking. Neither implements this server-side optimization.
Verification
Final source b56b828f83488a9343d40047a1790bea36dc3140:
vp test run src/peer/PeerLinks.test.ts src/peer/PeerForwarding.test.ts from apps/server: 19 tests pass.
“prefers a verified fallback briefly, rechecks identity, and retries the configured route” uses real HTTP peers and TestClock to cover reuse, fixed expiry, fresh identity, primary recovery, relink and unlink.
“starts the fallback preference window after route verification” holds a descriptor request at an explicit milestone, advances the clock two seconds, then proves the fallback remains preferred 59 seconds after verification and expires afterwards. It fails before the timestamp fix (another primary probe instead of reuse).
Existing reused-address and capability checks remain covered. Targeted lint/format, git diff --check, and server typecheck pass. No repo-wide checks were run.
Final-source remeasurement: actual resolver, SQLite, secrets, descriptor decoding and loopback HTTP sockets on Windows/Node24.18.0/Effect4.0.5, compared with fetched upstream main 5211acfe95a0c6d82a60e2524b5e46b47fe67a3e. Pairing excluded. Cold means first service resolution after pairing, not process startup. Same script/inputs, order main/final/final/main; three fresh service instances per healthy population per process, one per silent-primary population, each with one cold and three warm calls. Silent loopback address uses the real three-second timeout. This is controlled service timing, not real Tailscale/tunnel/UI latency.
Socket workload
n/version
Main median [range], ms
Final median [range], ms
Change
silent-primary, warm
6
3017.719 [3010.263, 3020.109]
15.079 [10.184, 16.212]
-99.50%
silent-primary, cold
2
3014.974 [3014.637, 3015.311]
3022.767 [3021.391, 3024.142]
+0.26%
healthy, cold
6
9.045 [7.696, 19.130]
15.188 [7.970, 21.851]
+67.91%
healthy, warm
18
14.846 [2.797, 17.052]
14.996 [4.821, 16.828]
+1.01%
healthy-multi, cold
6
12.045 [7.016, 15.988]
10.434 [5.727, 14.976]
-13.38%
healthy-multi, warm
18
15.505 [3.059, 16.399]
15.369 [3.232, 16.275]
-0.88%
Healthy measurements are noisy; no small JavaScript speedup is claimed. Earlier larger healthy-path diagnostics at 346e26e showed a +0.254ms/+10.86% multi-address warm cost when TCP/server time was removed; that healthy-primary path is unchanged by the timestamp correction. Retained-heap results vary with runtime/transport caches, so no whole-app memory or CPU saving is claimed. Real relay, browser rendering and native-client behavior remain unmeasured. This backend change has no UI screenshot.
Macroscope's review found this PR approvable — Linked-environment calls briefly prefer a verified fallback to avoid repeated timeout delays, while retaining fresh identity and credential checks. The bounded, in-memory preference expires after 60 seconds without changing saved configuration.
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Reviewing files that changed from the base of the PR and between 346e26e and b56b828.
Files selected for processing: 2
apps/server/src/peer/PeerLinks.test.ts
apps/server/src/peer/PeerLinks.ts
Files skipped from review as they are similar to previous changes: 2
apps/server/src/peer/PeerLinks.test.ts
apps/server/src/peer/PeerLinks.ts
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Walkthrough
Peer link resolution now remembers verified alternate URLs for 60 seconds and can try them before other configured URLs. It clears this preference after primary success, relinking, or unlinking. Tests cover fallback selection, route identity checks, delayed verification, and preference reset.
Changes: Peer route preference
Layer / File(s)
Summary
Record, reuse, and clear preferred routes apps/server/src/peer/PeerLinks.ts, apps/server/src/peer/PeerLinks.test.ts
Resolution reuses an eligible preferred alternate URL and records successful alternate routes for 60 seconds. It clears the preference after primary success, relinking, or unlinking. Tests cover delayed verification, fallback selection, identity checks, and link lifecycle.
No actionable merge-blocking issue is established for this change. Merge after normal checks.
Pre-merge checks: 4
Check name
Status
Explanation
Title check
The title clearly and concisely describes the main change: avoiding repeated timeouts for linked-environment calls through server-side route preference.
Description check
The description includes complete Problem, Change, Scope and approval, and Verification sections. It explains the behavior, scope, related issues, tests, measured results, limitations, and agent detai…
Linked Issues check
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Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Full details: Description check
Explanation
The description includes complete Problem, Change, Scope and approval, and Verification sections. It explains the behavior, scope, related issues, tests, measured results, limitations, and agent details.
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Actionable comments posted: 1
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Inline comments:
Review comments at @apps/server/src/peer/PeerLinks.ts:
- Around line 602-624: Update resolve to start the 60-second preference window
only after a fallback route has been verified: obtain the timestamp at that
point and use it to calculate the stored route’s until value instead of using
the timestamp captured before probing.
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Reviewing files that changed from the base of the PR and between 5211acf and 346e26e.
Files selected for processing: 2
apps/server/src/peer/PeerLinks.test.ts
apps/server/src/peer/PeerLinks.ts
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Problem
When a linked environment's first configured address stops responding but an alternate works, every forwarded RPC repeats the first address's full descriptor timeout.
PeerLinks.resolvestarts at the first configured URL on every call, even immediately after verifying a working fallback.Change
Prefer a verified fallback for a fixed 60 seconds after verification completes. Reuse does not extend the window. Expiry retries configured order; primary recovery, relinking and unlinking clear the preference. Starting the window after verification matters when several failed probes take a long time.
The map is allocated only after fallback use and capped at 256 entries containing a URL, credential-generation identifier and deadline. Every call still reads the link and credential, checks link expiry, and freshly checks peer identity and linked-agent limit capabilities. Healthy primary calls add no preference entry.
Tradeoff: a recovered preferred direct route can wait up to 60 seconds while the working fallback is used. The shared server resolver serves all clients/providers/MCP callers; no client UI, wire contract or provider adapter changes. Listing keeps its existing route order.
Scope and approval
Submitted under the small, focused obvious-defect exception: repeated full failed-route timeouts despite a freshly verified working alternate are the single defect addressed. This proposes that exception honestly; it does not claim maintainer approval or a triage exemption.
Open #26475 changes Tailscale address trust in the same resolver and needs coordination if both land. #24849 changes client socket stability; #26169 changes client route ranking. Neither implements this server-side optimization.
Verification
Final source
b56b828f83488a9343d40047a1790bea36dc3140:vp test run src/peer/PeerLinks.test.ts src/peer/PeerForwarding.test.tsfromapps/server: 19 tests pass.git diff --check, and server typecheck pass. No repo-wide checks were run.Final-source remeasurement: actual resolver, SQLite, secrets, descriptor decoding and loopback HTTP sockets on Windows/Node24.18.0/Effect4.0.5, compared with fetched upstream main
5211acfe95a0c6d82a60e2524b5e46b47fe67a3e. Pairing excluded. Cold means first service resolution after pairing, not process startup. Same script/inputs, order main/final/final/main; three fresh service instances per healthy population per process, one per silent-primary population, each with one cold and three warm calls. Silent loopback address uses the real three-second timeout. This is controlled service timing, not real Tailscale/tunnel/UI latency.Healthy measurements are noisy; no small JavaScript speedup is claimed. Earlier larger healthy-path diagnostics at
346e26eshowed a +0.254ms/+10.86% multi-address warm cost when TCP/server time was removed; that healthy-primary path is unchanged by the timestamp correction. Retained-heap results vary with runtime/transport caches, so no whole-app memory or CPU saving is claimed. Real relay, browser rendering and native-client behavior remain unmeasured. This backend change has no UI screenshot.Model: gpt-6.1-sol through Codex in T3 Code.