Build CLI records from typed Serialize structs (no post-construction Value mutation)

[flyingrobots]

Audit refs: AUD-2026-06-28-V03 §1.3 Violation 3 / Mitigation 6

diagnostic_record builds a json! object then mutates it by string index (record["span"] = …, record["line"] = …, record["message"] = …). Replace the diagnostic, check-result, and event record construction with typed #[derive(Serialize)] structs using #[serde(skip_serializing_if = "Option::is_none")] for optional fields.

Scope

• Introduce typed record structs; keep emitted bytes identical (serde_json preserves BTreeMap key order).
• Verify against the fixtures/cli/ golden corpus (byte-exact).

Acceptance criteria

• Records built from typed structs; golden corpus byte-identical; cargo xtask verify green.
• Update docs/audit/2026-06-28_ship-readiness.md §1.3 Violation 3: add ✅ Addressed (YYYY-MM-DD, #PR).

[coderabbitai]

🔗 Related PRs

#32 - docs: add workflow standards [merged]
#43 - Prepare v0.5.0-alpha.1 release [merged]
#67 - Add Echo Target IR lowering [merged]
#74 - Add JSON Schema contracts for all CLI stream record families [merged]

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