[v3/dev] Asset proxy exhausts host ephemeral ports on large frontends

[taliesin-ai]

Reproduction evidence

PR #5933 reports and measures the v3 development asset proxy exhausting the host ephemeral-port range when a large frontend serves many unbundled modules. The proxy transport retains only the Go default of two idle connections per host.

On macOS 26.2 with a large Vue frontend, the reporter measured:

• 13,511 TIME_WAIT sockets to the Vite port
• 16,299 / 16,384 ephemeral ports consumed (99.5%)
• 2,169 LAST_ACK and 1,650 FIN_WAIT_1 sockets
• zero established connections to the Vite port before the fix

After the focused pooling change, the same load produced zero TIME_WAIT sockets and about 52 retained connections. The synthetic regression test reports 597 upstream connections before the fix and 46–70 after it for 1,000 requests. Once exhausted, Wails, browsers, and unrelated CLI tools fail outbound connections with EADDRNOTAVAIL; the reporter required a reboot to clear the backlog.

Scope and impact

This is development-only (build_dev.go is excluded by the production build tag), but it can disrupt every process on the host and makes large Wails projects effectively unusable in wails3 dev. The release work is limited to reviewing and validating the existing focused fix in #5933; do not broaden it into retry-policy changes.

Acceptance criteria

• The dev proxy reuses upstream connections under concurrent module loads.
• Idle connection retention is explicitly bounded and timed out.
• Address-exhaustion failures are not amplified by the retry classifier.
• Focused tests prove connection reuse and production-tag builds remain unaffected.
• Current-master integration and relevant hosted checks pass.
• Existing PR fix(v3): stop the dev asset proxy exhausting the host's ephemeral ports #5933 is used; no duplicate implementation PR is created.

Related implementation: #5933.

[coderabbitai]

🔗 Related PRs

#5265 - fix(v3/windows): fixes the 502 Bad Gateway errors that occur when using Vite as the frontend dev server in development mode [merged]
#5365 - fix(v3): configure Vite port via env var so pnpm (and other package managers) work in dev mode [merged]
#5776 - fix(dev): fix frontend dev server startup race [open]
#5828 - fix: dev frontend readiness [open]
#5933 - fix(v3): stop the dev asset proxy exhausting the host's ephemeral ports [open]

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[taliesin-ai]

Release validation evidence for PR #5933 at 9a0181b: focused reuse/retry tests passed 10 repeated runs with CGO disabled; the same focused tests passed twice under the race detector using a file-mode package build; the production-tag assetserver build, broader root assetserver tests, go vet, and git diff check passed. A synthetic no-commit merge with current origin/master a0fae83 conflicted only in v3/UNRELEASED_CHANGELOG.md; after preserving both entries, all critical tests passed. CodeRabbit CLI reported no findings and the PR was approved. Native Linux package compilation on this runner lacks GTK4/WebKitGTK development packages, so that exact CGO-enabled package command remains unverified locally. Current blocker: the contributor branch must be rebased or updated to resolve the changelog conflict; Project 16 correctly remains In Progress.

[taliesin-ai]

Verified independently on current origin/master snapshot aa3e48fdc: merge 9a8800b71 from #5933 is an ancestor and the worktree is clean. Local release validation passed:

• focused proxy-reuse/address-exhaustion tests: 10/10 repetitions; 44–60 upstream connections per 1,000 requests (limit 128)
• focused race run: 3/3 repetitions; 39–51 connections per 1,000 requests
• complete ./internal/assetserver suite
• -tags production assetserver test/build
• vet in both default and production-tag configurations
• git diff --check and git diff --exit-code

The merged transport explicitly bounds the per-host idle pool at 512 with a 90s idle timeout, and address-exhaustion errors remain fail-fast. PR #5933 hosted checks are green. Acceptance criteria are satisfied.