Add CTO Case candidate PRD

CONTEXT.md

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+# Cortex OS CTO Context
+
+This context defines local product language for the Cortex OS CTO planning workspace.
+It is child-local glossary language and does not create Core authority.
+
+## Language
+
+**CTO Product Surface**:
+A governed operator-facing product area for delegating bounded code-change work while preserving Cortex OS authority, evidence, and approval rules.
+_Avoid_: CTO app, autonomous developer, coding bot
+
+**Case Candidate Backend**:
+The proposed Case-based execution backend for real-repo code-change work, admitted only after adapter proof, validator coverage, and governed routing.
+_Avoid_: Case default, Case authority, replacement kernel
+
+**CTO Harness**:
+The adapter conformance and evidence validation module that normalizes backend behavior into a stable CTO evidence interface.
+_Avoid_: execution authority, final reviewer, product readiness proof
+
+**Harness Evidence Interface**:
+The stable artifact and event contract used to compare backends and prove bounded execution results.
+_Avoid_: loose evidence bundle, backend logs, success claim
+
+**Target Repository**:
+The owned source repository receiving bounded, approved, evidence-producing code changes.
+_Avoid_: vendor source, hidden workspace, disposable scratch by default