feat: headroom wrap opencode / unwrap opencode CLI (#1105)

## Summary

This PR implements transparent `headroom wrap opencode` support without
asking users to edit OpenCode provider URLs, choose an extra CLI flag,
or maintain a static provider list.

The wrapper now lives at the runtime transport boundary: OpenCode keeps
its user/provider config, while Headroom intercepts outbound provider
traffic in-process and routes it through the local Headroom proxy.

## What changed

### Transparent OpenCode wrapping

- `headroom wrap opencode` injects the `headroom-opencode` plugin
through `OPENCODE_CONFIG_CONTENT`.
- Existing OpenCode provider URLs are preserved. We do not rewrite user
config URLs to point at Headroom.
- Existing `OPENAI_BASE_URL` and `ANTHROPIC_BASE_URL` env vars are
preserved.
- Local OpenCode traffic, localhost traffic, and Headroom proxy traffic
bypass the shim to avoid loops.

### Runtime transport interception

- Added an OpenCode plugin transport shim that wraps:
  - `globalThis.fetch`
  - `http.request` / `http.get`
  - `https.request` / `https.get`
- External provider calls are routed to the local Headroom proxy.
- The original upstream origin is passed through `x-headroom-base-url`,
so the proxy can forward to the real provider without changing OpenCode
config.
- External `http2.connect` is blocked loudly instead of allowing direct
provider traffic to leak outside Headroom.

### Live provider additions

Provider coverage is no longer based on a static config scan. Because
routing happens at outbound request time, providers added mid-session
are routed through Headroom automatically as long as they use the
covered Node transport paths.

### Subagent and child-process coverage

- The parent OpenCode plugin sets a packaged Node preload shim through
`NODE_OPTIONS=--import=.../hook-shim/handler.js`.
- The transport shim patches `child_process.spawn`, `exec`, `execFile`,
and `fork` so child Node processes receive the Headroom preload even
when OpenCode passes a custom `env`.
- The child-process shim fails closed if it loads without
`HEADROOM_OPENCODE_TRANSPORT_PROXY_URL`.
- This closes the subagent leak path where a child Node process could
otherwise start without Headroom transport interception.

## Why this goes beyond PR #1089

PR #1089 improves OpenCode provider registration, but it still focuses
on provider config shape. This PR moves the enforcement boundary to
runtime transport interception.

This PR goes further because:

- No provider URL rewriting is required.
- New providers added mid-session are covered automatically.
- Subagents and child Node processes inherit the Headroom transport
shim.
- Direct external HTTP/2 paths fail loudly instead of leaking.
- The wrap remains transparent to the user's OpenCode provider config.
- The wrapper is fail-closed for unsupported child-process preload
state.

## Additional robustness fixes

While validating the change in Docker, the full Python suite exposed
unrelated Linux/container robustness issues. These are fixed in this PR
so the suite is green:

- Binary cache handling now treats cache paths under a non-writable
existing parent as unavailable, including when tests run as root in
Docker.
- `release_version.py` honors `MANUAL_VER` before git calls so direct
script execution works outside a `.git` checkout.
- Test logger isolation now resets relevant Headroom child loggers so
proxy logging setup cannot poison later `caplog` tests.
- The scanner missing-path test now uses a guaranteed missing `tmp_path`
child instead of relying on `/nonexistent/path`.

## Validation

All implementation validation was run inside Docker.

- Full Python suite from a fresh Docker copy: `6605 passed, 523
skipped`.
- Ruff on changed Python/OpenCode paths: passed.
- OpenCode plugin typecheck: passed.
- OpenCode plugin tests: `9 passed`.
- OpenCode plugin build: passed.
- Hook shim preload smoke test: passed.

## Notes

This PR intentionally does not add a CLI option. `headroom wrap
opencode` means full wrap. Either Headroom wraps OpenCode transparently,
or the path fails loudly instead of silently leaking provider traffic.

---------

Co-authored-by: Rudimar Ronsoni <6081613+rudironsoni@users.noreply.github.com>

scripts/install.ps1

@@ -1611,7 +1611,7 @@ switch ($args[0]) {
         }
 
         if ($args.Count -lt 2) {
-            Fail 'Usage: headroom wrap <claude|codex|aider|cursor|openclaw> [...]'
+            Fail 'Usage: headroom wrap <claude|codex|aider|cursor|openclaw|opencode> [...]'
         }
 
         $tool = $args[1]
@@ -1623,8 +1623,9 @@ switch ($args[0]) {
             'aider' { }
             'cursor' { }
             'openclaw' { }
+            'opencode' { }
             default {
-                Fail "Docker-native wrapper does not support 'wrap $tool'. Supported targets: claude, codex, aider, cursor, openclaw"
+                Fail "Docker-native wrapper does not support 'wrap $tool'. Supported targets: claude, codex, aider, cursor, openclaw, opencode"
             }
         }