fix(windows): preserve provider launch environment and test native shims

CHANGELOG.md

@@ -7,6 +7,11 @@ Versioning and Keep a Changelog conventions.
 
 ### Changed
 
+- Preserve Windows system and profile environment variables when launching providers,
+  without inheriting unrelated credentials. Hide provider and cleanup console windows.
+  Add native process fixtures for arguments, stdin, failures, cancellation, and
+  Windows Claude/Codex/OpenCode `.cmd` wrappers.
+
 - Corrected the minimum supported Rust version to 1.88 to match locked
   dependencies, with an all-targets/all-features compiler check in CI.
 - Crate archive paths are root-anchored so nested third-party README/license

CONTRIBUTING.md

@@ -47,3 +47,8 @@ Keep pull requests focused and describe:
 
 By contributing, you agree that your contributions are licensed under the
 project's MIT OR Apache-2.0 terms.
+
+## Platform compatibility
+
+See [Linux and Windows runtime testing](docs/how-to/test-platform-compatibility.md)
+for native launch fixtures and the separate authenticated-provider acceptance checks.

docs/how-to/manage-background-processes.md

@@ -107,3 +107,11 @@ For agent-launched descendants, see
 [Keep tool processes running](keep-tool-processes-running.md). For durable
 projection rules, see
 [Persist command and tool execution](persist-command-execution.md).
+
+### Provider server shutdown
+
+For attached providers such as `opencode serve`, the runtime stops the server
+after a terminal protocol event. A signal or nonzero exit caused by that
+intentional shutdown does not turn a completed turn into a failure. Provider
+errors and an unexpected stream closure still fail the turn; cancellation
+continues to abort the session before terminating its process.

docs/how-to/test-platform-compatibility.md

@@ -0,0 +1,59 @@
+# Test Linux and Windows runtime compatibility
+
+Run native process tests on the execution host, not only on the desktop client.
+The runtime launches the provider CLI on that host. A Windows Fleet client
+connected to a Linux execution target does not exercise native Windows agents.
+
+## Credential-free launch tests
+
+Install stable Rust and run:
+
+```sh
+cargo test --locked --lib process::tests -- --nocapture
+cargo test --locked --all-features
+```
+
+The process tests compile a small native executable in a directory containing
+spaces. They verify JSON and Unicode arguments, stdin, explicit environment
+values, nonzero exit status, and cancellation. Windows additionally launches
+`claude.cmd`, `codex.cmd`, and `opencode.cmd` fixture wrappers. These are launcher
+fixtures, not actual authenticated provider turns. No provider installation or
+model credentials are needed. The existing CI matrix runs these tests on Linux,
+macOS, and Windows.
+
+The SDK preserves an explicit environment allowlist. On Windows this includes
+system paths and profile/configuration directories, using case-insensitive key
+matching. Unrelated API keys are not inherited. Explicit command environment
+values still override inherited values. Windows child launches and taskkill
+cleanup suppress console windows. Rust owns native command argument escaping;
+callers must supply separate program and argument values.
+
+## Real provider acceptance
+
+Before claiming full platform support, run each installed provider through the
+SDK on Linux and Windows with the user's own login. Verify tool start/completion,
+approvals, cancellation with descendant processes, session resume, missing or
+expired authentication, and long-running development servers. Exercise both
+native executable and npm shim installations on Windows. Run equivalent tests
+through Fleet after its adapter correctly maps the SDK's launch capabilities.
+A successful cross-compilation or fixture run does not certify these journeys.
+
+## Current limits
+
+- SSH password authentication from a Windows execution host is explicitly
+  unsupported; the askpass helper currently requires Unix.
+- Process-tree cleanup uses Unix process groups or Windows `taskkill /T /F`.
+  This is lifecycle management, not a security sandbox.
+- Sandbox backend support must be checked independently; never bypass a requested
+  sandbox to make a platform test pass.
+- Windows OS-service installation is an application responsibility, outside
+  this library's provider launch contract.
+
+Real CLI checks now also cover extensionless npm command names on Windows,
+resolved against the child PATH before spawning. OpenCode serve readiness uses
+`/global/health` and requires a healthy JSON response; `/app` is a web UI route
+in current versions and is not an API readiness check. Each probe is bounded.
+
+Fleet launch-context checks include additional developer instructions on new
+and resumed Codex app-server threads; this preserves Fleet model identity
+instructions without rejecting the first turn before it reaches the provider.