Define CODE and CODEX compatibility naming policy

[shiny-code-bot]

Objective

Define and apply a compatibility-safe policy for CODE_*, CODEX_*, ~/.code, and ~/.codex names.

Current Status

State: Waiting
Next action: Decide which env names get aliases, which dev-only names can rename, and which compatibility names must stay.
Blocked by: Owner decision on compatibility window and backend/external dependency tolerance.
Last verified: 2026-05-28.

Finish Line

Env/config compatibility names are classified and safely aliased or preserved

Acceptance Criteria

• Preserve CODEX_HOME / ~/.codex compatibility fallback unless a separate migration says otherwise.
• Classify CODEX_TUI_* debug/test vars as rename, alias, or keep.
• Classify runtime/security/backend vars such as secure mode/API-key/header names before edits.
• Document alias order and deprecation posture.
• Add tests for any env-var behavior changes.

Relationships

Sub-issue of #179.
Related to #130 cleanup.

[shiny-code-bot]

Completed in PR #194. The CODE/CODEX compatibility policy is now documented in docs/upstream-import-policy.md, linked from AGENTS.md and docs/config.md, and the preserved CODEX_API_KEY / CODEX_TUI_* posture is documented without changing runtime behavior. Validation passed locally with git diff --check and ./build-fast.sh; main Release run 26612168610 passed 8/8.