Require global Git config access for daemon startup

[svarlamov]

Summary

Require daemon startup to have a readable global Git configuration.

• Validate only global config with one bounded git config --global --list invocation.
• Do not inspect repository-local config.
• Reject startup when the global config is absent, inaccessible, or invalid.
• Keep the probe outside trace2 ingestion and reuse the existing trace2-disabled Git execution helper.

Why use Git directly

Git is the source of truth for config path resolution, parsing, and include behavior. A gix preflight added complexity without improving the intended contract: the daemon requires the global config to exist and be readable. The probe runs once at daemon startup, never on the latency-sensitive ingestion path, and has a fixed process bound.

Tests and fixtures

Strict TDD coverage demonstrates that:

• an inaccessible global config rejects both daemon start and daemon run;
• an absent global config rejects startup;
• an inaccessible repository-local config does not block startup.

Isolated TestRepo homes contain an empty global config by default, matching the installed-product prerequisite; negative tests explicitly remove or replace it. The nasty benchmark fixture likewise creates the GIT_CONFIG_GLOBAL file before starting its isolated daemon.

Validated with:

• task test TEST_FILTER=git_config
• focused benchmark daemon-start smoke
• task fmt
• task lint
• task test

[svarlamov]

• Require global Git config access for daemon startup #1972 👈 (View in Graphite)
• main

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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