Sanitize remote execution envs at the boundary (#5325)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Adapters spawn CLIs against local, SSH, and sandbox targets,
threading a runtime env through `runAdapterExecutionTargetProcess` and
the SSH/sandbox runners
> - Host identity vars (HOME, TMPDIR, XDG_*, NVM_DIR, PATH) routinely
leak into the env we send to remote targets — sometimes via test probes,
sometimes via runtime config — and break sandboxed/SSH'd CLIs whose own
profiles set those values correctly
> - The sanitization logic existed but lived alongside other helpers in
`server-utils.ts` and was applied piecemeal at adapter callsites, so it
was easy to bypass
> - This pull request lifts the sanitization into a standalone
`remote-execution-env.ts`, applies it at the SSH and sandbox runtime
boundary so every remote spawn goes through it, and removes the
duplicated callsite-level filtering
> - The benefit is identity-bound host env stops leaking across
SSH/sandbox transports regardless of which adapter calls in

## What Changed

- `packages/adapter-utils/src/remote-execution-env.ts`: new module —
single source of truth for which env keys are identity-bound and how to
strip them when the value matches the host's value
- `packages/adapter-utils/src/server-utils.ts`: remove the inline
sanitization (now in `remote-execution-env.ts`)
- `packages/adapter-utils/src/execution-target.ts`: apply sanitization
at the sandbox runtime boundary
- `packages/adapter-utils/src/ssh.ts`: apply sanitization at the SSH
spawn boundary
- `packages/adapters/opencode-local/src/server/test.ts`: drop
now-redundant callsite filtering
- `packages/adapters/pi-local/src/server/test.ts`: drop now-redundant
callsite filtering
- New tests `execution-target.test.ts` and
`execution-target-sandbox.test.ts` cover the sanitizer flow at both
transports, including positive cases (host-shaped path stripped) and
explicit-override preservation

## Verification

- `pnpm vitest run --no-coverage --project @paperclipai/adapter-utils
--project @paperclipai/adapter-opencode-local --project
@paperclipai/adapter-pi-local`
- `pnpm typecheck` clean

## Risks

Low–medium. The sanitization is now applied at one layer (boundary)
instead of N (callsites), so behavior is more consistent. Any adapter
that previously relied on a leaked host var landing on the remote shell
would now see it stripped — but those reliances were what this change
exists to fix.

## Model Used

Claude Opus 4.7 (1M context)

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable — new tests at both
transports
- [x] If this change affects the UI, I have included before/after
screenshots — N/A (no UI)
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

packages/adapters/opencode-local/src/server/test.ts

@@ -290,13 +290,6 @@ export async function testEnvironment(
       if (variant) args.push("--variant", variant);
       if (extraArgs.length > 0) args.push(...extraArgs);
 
-      // For remote targets, do NOT spread the host process.env into the
-      // probe env: it leaks macOS-only paths (HOME=/Users/..., host
-      // XDG_CONFIG_HOME, TMPDIR, etc.) into the remote shell, which causes
-      // opencode on the remote box to try to mkdir host paths like /Users.
-      // Match the pattern used by claude_local / codex_local / gemini_local
-      // probes: send only the user-configured adapter env across SSH.
-      const probeEnv = targetIsRemote ? preparedRuntimeConfig.env : runtimeEnv;
       try {
         const probe = await runAdapterExecutionTargetProcess(
           runId,
@@ -305,7 +298,7 @@ export async function testEnvironment(
           args,
           {
             cwd,
-            env: probeEnv,
+            env: runtimeEnv,
             timeoutSec: 60,
             graceSec: 5,
             stdin: "Respond with hello.",