fix(envd): avoid Start deadlock after request cancellation

[arkamar]

Start sent its bootstrap event directly to the unbuffered channel returned by MultiplexedChannel.Fork. If the stream sender observed request cancellation first, no receiver remained and the handler blocked on the send, preventing its process-event subscriptions from being released.

Replace the unnecessary single-subscriber multiplexer with a one-slot channel so bootstrap publication cannot block after cancellation. The regression test exercises this ordering through the Connect handler and verifies that server shutdown is no longer held open by the stuck request.

[cursor]

PR Summary

Medium Risk
Touches concurrency and lifecycle of a core streaming RPC path; behavior change is narrow but cancellation ordering is easy to get wrong without the new test.

Overview
Fixes a deadlock in the process Start stream when the request context is cancelled before the bootstrap start event is consumed: the handler could block forever on publishing that event, leaving connections open and blocking server shutdown.

The bootstrap path no longer uses a single-subscriber multiplexer on an unbuffered fork; it uses a one-slot buffered channel so emitting the start event cannot block after the sender goroutine has already exited on cancellation. A regression test cancels the request at handler entry and asserts httptest server close completes within a timeout. Version bumps to 0.6.10.

^{Reviewed by Cursor Bugbot for commit 843de1c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[gemini-code-assist]

Code Review

This pull request replaces a multiplexed channel with a buffered channel of size 1 in handleStart to prevent blocking when a receiver goroutine exits early due to a cancelled context. It also updates the test helper newTestService to support middleware and adds a new test TestStart_CancelBeforeStartEvent to verify this behavior. Feedback was provided regarding the middleware wrapping order in the test helper, which currently executes middlewares in reverse (right-to-left) order.

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[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
3260	1	3259	9

View the top 3 failed test(s) by shortest run time

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_1_lists_root_directory

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_1_lists_root_directory
=== PAUSE TestListDir/depth_1_lists_root_directory
=== CONT  TestListDir/depth_1_lists_root_directory
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_1_lists_root_directory
--- FAIL: TestListDir/depth_1_lists_root_directory (0.01s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
=== PAUSE TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
=== CONT  TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
--- FAIL: TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory) (0.01s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_0_lists_only_root_directory

Stack Traces | 0.02s run time

=== RUN   TestListDir/depth_0_lists_only_root_directory
=== PAUSE TestListDir/depth_0_lists_only_root_directory
=== CONT  TestListDir/depth_0_lists_only_root_directory
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_0_lists_only_root_directory
--- FAIL: TestListDir/depth_0_lists_only_root_directory (0.02s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir

Stack Traces | 0.81s run time

=== RUN   TestListDir
=== PAUSE TestListDir
=== CONT  TestListDir
--- FAIL: TestListDir (0.81s)
Executing command cat in sandbox iqaic6su598z03cn9jckf (user: root)

github.com/e2b-dev/infra/tests/integration/internal/tests/api/sandboxes::TestEgressFirewallDomainCaseInsensitive

Stack Traces | 3.74s run time

=== RUN   TestEgressFirewallDomainCaseInsensitive
=== PAUSE TestEgressFirewallDomainCaseInsensitive
=== CONT  TestEgressFirewallDomainCaseInsensitive
Executing command curl in sandbox imhnamkt0u557u86wj0et
    sandbox_network_out_test.go:68: Command [curl] output: event:{start:{pid:1081}}
    sandbox_network_out_test.go:68: Command [curl] output: event:{data:{stdout:"HTTP/2 301 \r\nlocation: https://www.google.com/\r\ncontent-type: text/html; charset=UTF-8\r\ncontent-security-policy-report-only: object-src 'none';base-uri 'self';script-src 'nonce-HGQt1XY1dkdnlLBZM378ug' 'strict-dynamic' 'report-sample' 'unsafe-eval' 'unsafe-inline' https: http:;report-uri https://csp.withgoogle..../csp/gws/other-hp\r\ndate: Fri, 10 Jul 2026 15:22:02 GMT\r\nexpires: Sun, 09 Aug 2026 15:22:02 GMT\r\ncache-control: public, max-age=2592000\r\nserver: gws\r\ncontent-length: 220\r\nx-xss-protection: 0\r\nx-frame-options: SAMEORIGIN\r\nalt-svc: h3=\":443\"; ma=2592000,h3-29=\":443\"; ma=2592000\r\n\r\n"}}
    sandbox_network_out_test.go:68: Command [curl] output: event:{end:{exited:true status:"exit status 0"}}
    sandbox_network_out_test.go:68: Command [curl] completed successfully in sandbox i1cg8l6bersb7esjd6n7m
Executing command curl in sandbox i1cg8l6bersb7esjd6n7m
    sandbox_network_out_test.go:651: Command [curl] output: event:{start:{pid:1083}}
    sandbox_network_out_test.go:651: 
        	Error Trace:	.../api/sandboxes/sandbox_network_out_test.go:78
        	            				.../api/sandboxes/sandbox_network_out_test.go:651
        	Error:      	"failed to execute command curl in sandbox i1cg8l6bersb7esjd6n7m: invalid_argument: protocol error: incomplete envelope: unexpected EOF" does not contain "failed with exit code"
        	Test:       	TestEgressFirewallDomainCaseInsensitive
        	Messages:   	Expected connection failure message
Executing command curl in sandbox il50sapidnyzn8l73i7nn
--- FAIL: TestEgressFirewallDomainCaseInsensitive (3.74s)

github.com/e2b-dev/infra/tests/integration/internal/tests/proxies::TestMaskRequestHostAPIParameter

Stack Traces | 5.08s run time

=== RUN   TestMaskRequestHostAPIParameter
=== PAUSE TestMaskRequestHostAPIParameter
=== CONT  TestMaskRequestHostAPIParameter
    mask_request_host_test.go:44: Command [python3] output: event:{start:{pid:1138}}
    mask_request_host_test.go:68: Command [cat] output: event:{start:{pid:1139}}
    mask_request_host_test.go:68: Command [cat] output: event:{data:{stderr:"cat: /tmp/nc_output.txt: No such file or directory\n"}}
    mask_request_host_test.go:68: Command [cat] output: event:{end:{exit_code:1 exited:true status:"exit status 1" error:"exit status 1"}}
    mask_request_host_test.go:69: 
        	Error Trace:	.../tests/proxies/mask_request_host_test.go:69
        	Error:      	Received unexpected error:
        	            	command cat in sandbox i7vofmnxkugkqqn42giio failed with exit code 1
        	Test:       	TestMaskRequestHostAPIParameter
--- FAIL: TestMaskRequestHostAPIParameter (5.08s)

View the full list of 1 ❄️ flaky test(s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_3_lists_all_directories_and_files

Flake rate in main: 30.77% (Passed 9 times, Failed 4 times)

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_3_lists_all_directories_and_files
=== PAUSE TestListDir/depth_3_lists_all_directories_and_files
=== CONT  TestListDir/depth_3_lists_all_directories_and_files
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_3_lists_all_directories_and_files
--- FAIL: TestListDir/depth_3_lists_all_directories_and_files (0.01s)

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[claude]

Small, targeted deadlock fix with a solid regression test.

Extended reasoning...

Overview

Touches only packages/envd/internal/services/process/start.go (~10 lines), a new regression test in start_test.go, and the required envd version bump (0.6.9 → 0.6.10). The fix replaces handler.MultiplexedChannel — which was being used with a single subscriber — with a plain chan rpc.ProcessEvent_Start of buffer 1. This ensures the bootstrap send after proc.Start() can never block if the sender goroutine has already exited via ctx.Done().

Security risks

None. The change is confined to intra-handler goroutine synchronization inside envd; no auth, crypto, or network-visible surface is affected.

Level of scrutiny

Low-to-moderate. Envd runs inside guest microVMs and the handler is on a well-trafficked code path, but the semantic change is narrow: buffered channel semantics for a single-shot bootstrap event. Correctness verified by inspection — if the sender goroutine wins ctx.Done(), the buffered event is silently dropped (correct, since the client has disconnected); if it wins the start path, behavior is identical to before. The <-exitChan join at the end still guarantees the outer handler waits for the sender.

Other factors

The regression test cancels the request context at HTTP handler entry via middleware, which reliably exercises the racing ordering, and bounds the server close in a goroutine with a 20s watchdog — a stuck handler would fail loudly. The PR description accurately describes both the bug and the fix. No outstanding reviewer feedback.