fix(claude): stop forcing tool search on Foundry

[rodboev]

Description

Foundry sessions launched through headroom wrap claude currently receive Headroom's generic ENABLE_TOOL_SEARCH=true default when the user did not choose a tool-search mode. That can push Claude Code into a deferred-tool request shape that Azure Foundry rejects with API Error: 400 ... Some tools are not available. This narrows the default-only path so Foundry sessions stop forcing deferred-tool mode when the user did not ask for it, while explicit overrides and the existing non-Foundry custom-host behavior stay unchanged.

Closes #2464

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Performance improvement
• Code refactoring (no functional changes)

Changes Made

• add a Foundry-specific default for the no-override tool-search branch
• preserve explicit --tool-search values and pre-set ENABLE_TOOL_SEARCH values exactly
• keep the generic non-Foundry default as true
• add focused helper-level regression coverage for Foundry defaulting and adjacent negative space

Testing

• Focused unit tests pass (uv run pytest tests/test_cli/test_wrap_claude.py tests/test_cli/test_wrap_claude_vertex_proxy_env.py tests/test_issue_746_tool_search.py -q)
• Edited-file linting passes (uv run ruff check headroom/cli/wrap.py headroom/providers/claude/runtime.py tests/test_cli/test_wrap_claude.py)
• Type checking passes (uv run mypy headroom)
• New tests added for new functionality when applicable
• Manual testing performed

Test Output

Command: uv run pytest tests/test_cli/test_wrap_claude.py tests/test_cli/test_wrap_claude_vertex_proxy_env.py tests/test_issue_746_tool_search.py -q
61 passed

Command: uv run ruff check headroom/cli/wrap.py headroom/providers/claude/runtime.py tests/test_cli/test_wrap_claude.py
All checks passed!

Real Behavior Proof

• Environment: Windows, Python via uv, Foundry mode modeled through the wrap helper inputs
• Exact command / steps: run the focused helper regression and edited-file lint commands above
• Observed result: 61 passed; All checks passed!; Foundry mode without an override writes ENABLE_TOOL_SEARCH=false, while explicit overrides, existing values, blank handling, and the non-Foundry default remain covered
• Not tested: live Azure Foundry tenant run

Review Readiness

• I have performed a self-review
• This PR is ready for human review

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the CHANGELOG.md if applicable

Additional Notes

CHANGELOG.md stays untouched because Headroom generates release notes from conventional commits. Live Foundry proof is intentionally left to a real tenant run; the code and focused tests only claim the launch-mode change inside Headroom.

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[JerrettDavis]

Reviewed the latest diff against upstream main. The Foundry-specific default is scoped to the no-override path, preserves explicit/pre-existing ENABLE_TOOL_SEARCH values, and keeps the non-Foundry default unchanged. I also checked the adjacent Remote Control sibling-note path; it is only reached on the non-Foundry branch, so the new Foundry default does not make that banner inaccurate.

Local verification: uv run pytest tests/test_cli/test_wrap_claude.py tests/test_cli/test_wrap_claude_vertex_proxy_env.py tests/test_issue_746_tool_search.py -q -> 61 passed.