## Description
Claude Code disables on-demand tool loading (Tool Search) when
`ANTHROPIC_BASE_URL` is a custom host and `ENABLE_TOOL_SEARCH` is unset,
materializing all MCP/system tool schemas into its context window
(#746). With many MCP servers this overflows the window — breaking
sub-agent spawns ("prompt too long, ~214k > 200k") and forcing constant
compaction. `headroom wrap claude` already sets it; `init`/install did
not. Refs #746.
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
## Changes Made
- Keep tool deferral on at both entry points, sharing one
`TOOL_SEARCH_ENV` / `TOOL_SEARCH_DEFAULT` constant from the Claude
provider package (`providers/claude/runtime.py`) so the key/default
can't drift:
- `init` (`_ensure_claude_hooks`): sets `ENABLE_TOOL_SEARCH=true` via
`setdefault`, respecting a pre-existing user-provided value.
- `install` (`build_install_env`): always writes
`ENABLE_TOOL_SEARCH=true`. This is the headroom-managed install env
(recorded and reverted on uninstall), so it is authoritative rather than
deferring to an existing value.
## Testing
- [x] Unit tests pass (`pytest`)
- [x] New tests added for new functionality
- [x] Manual testing performed
### Test Output
```text
$ pytest tests/test_cli/test_init_enable_tool_search.py -q
3 passed in 0.63s
```
## Real Behavior Proof
- Environment: Python 3.14, headroom proxy on :8799, ~19 MCP servers
connected
- Exact command / steps: launched `claude` through the proxy with vs
without `ENABLE_TOOL_SEARCH=true`, asked each to spawn 5 parallel
sub-agents
- Observed result: without it, all 5 sub-agents fail ("prompt too long,
~214k > 200k"); with `ENABLE_TOOL_SEARCH=true` all 5 succeed and traffic
compresses
- Not tested: non-Claude-Code agents
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
