fix(dotnet): end the bridge socket on netcoredbg's close, not its exit (#878)

[debugmcpdev]

Summary

Fixes #878.

packages/adapter-dotnet/src/utils/netcoredbg-bridge-core.ts ended the proxy's socket on the child's exit event. Node fires exit when the process ends and close once its stdio streams have drained, so an output / exited / terminated frame netcoredbg wrote just before exiting could still be in the stdout pipe when the socket was closed — the same class as #860 ("last line before exit"). The Dart bridge (dap-stdio-bridge-core.ts) already carries the rule; this brings the netcoredbg bridge in line.

Changes

• The socket is ended on the child's close, never on exit (exit only marks the child gone).
• Once the child has exited, proxy bytes aimed at its stdin are dropped instead of written to a dead pipe, and an in-flight stdin error (EPIPE) is logged to the bridge's stderr instead of crashing the bridge — there was no stdin error listener before.
• dotnet-utils.ts header: replaced "netcoredbg natively supports DAP over TCP … No bridge process is needed" with what the bridge is for; packages/adapter-dotnet/docs/dotnet-adapter.md no longer says the --server bug is Windows-only (its own next paragraph said all platforms).
• changelog.d/878.fixed.md.

Tests (packages/adapter-dotnet/tests/unit/netcoredbg-bridge-core.test.ts, 9 → 12)

• keeps the socket open across netcoredbg exit until its streams close, then ends it (issue #878) — emits exit, then a final Content-Length: 2\r\n\r\n{} on stdout, then close; asserts the client received the frame. Red before the fix: the client received '' (the frame was lost to the ended socket, which also raised ERR_STREAM_WRITE_AFTER_END into the socket error path).
• stops forwarding socket bytes to netcoredbg stdin once it has exited (red before: the write went through).
• logs a netcoredbg stdin error instead of dying on it (red before: unhandled error on stdin).
• The existing cleans up on netcoredbg exit emitted only exit and would hang under the new rule; it now emits exit then close (cleans up once netcoredbg has closed).

Verification

• pnpm exec vitest run --project unit packages/adapter-dotnet/tests — 170 passed.
• npm run typecheck:all (ratchet 0/0), eslint on the touched files, pnpm changelog:check, node scripts/check-docs.mjs — clean.
• Pre-push hook (unit + integration) passed.

Not observed live (the issue notes netcoredbg usually answers disconnect and lingers); the unit test is the reproduction of the race.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...adapter-dotnet/src/utils/netcoredbg-bridge-core.ts	92.30%	1 Missing ⚠️

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