docs(spec): clarify invariant CLI completeness requirements

UAT findings #7461 and #7462 identified two spec-implementation gaps in
the invariant system:

1. Missing --non-overridable CLI flag (#7461):
   The spec defines 'agents invariant add --global --non-overridable'
   but the CLI raises 'No such option: --non-overridable'. System
   administrators cannot create non-overridable global safety constraints.

2. Action-scope omitted from --effective output (#7462):
   The spec defines four-tier precedence (plan > action > project > global)
   but InvariantService.get_effective_invariants() only merges plan/project/
   global, omitting action scope entirely. The --effective output also
   ignores non_overridable semantics.

Added 'CLI completeness requirements for invariants' section clarifying:
- --non-overridable flag MUST be implemented (global scope only)
- Action-scope MUST be included in --effective output
- non_overridable semantics MUST be correctly applied in --effective

Refs: UAT #7461, UAT #7462

docs/specification.md

@@ -19748,6 +19748,14 @@ Each effective invariant is then recorded as an `invariant_enforced` decision in
 
 **Non-overridable global invariants**: A global invariant may be marked `non_overridable: true`. When set, this invariant takes precedence over all lower-scope invariants regardless of the normal precedence chain -- even plan-level invariants cannot override it. This is intended for system-wide safety constraints that must never be relaxed (e.g., "Never commit secrets to version control"). Non-overridable invariants are set via `agents invariant add --global --non-overridable "<constraint>"`. The `non_overridable` flag is only meaningful on `GLOBAL`-scoped invariants; it is ignored on project, action, and plan invariants.
 
+**CLI completeness requirements for invariants**:
+
+1. **`--non-overridable` flag**: The `agents invariant add --global --non-overridable "<text>"` command MUST be implemented. Without this flag, system administrators cannot create non-overridable global safety constraints, making the safety override feature effectively unusable. The flag is only accepted when combined with `--global`; using it with `--project`, `--action`, or `--plan` MUST raise a validation error.
+
+2. **Action-scope in `--effective` output**: The `agents invariant list --effective` command MUST include action-scope invariants in the effective set. The four-tier precedence is `plan > action > project > global` — action-scope invariants sit between plan and project scope. Omitting action-scope invariants from the effective view causes the CLI output to disagree with the Invariant Reconciliation Actor used during Strategize, making `--effective` unreliable for UAT validation.
+
+3. **`non_overridable` in `--effective` output**: The `--effective` output MUST correctly apply `non_overridable` semantics. When a global invariant has `non_overridable: true`, it MUST appear at the top of the effective set and MUST NOT be overridden by plan-scope invariants, even when a plan-scope invariant would normally take precedence. The output MUST indicate which invariants are non-overridable (e.g., via a `[NON-OVERRIDABLE]` marker or a dedicated column).
+
 **Child plan inheritance**: When a top-level plan spawns child plans, the parent's effective invariant view (already reconciled) is passed down to each child plan. Child plans do not re-run reconciliation — they inherit the parent's resolved view.
 
 **Correcting invariants**: The correction mechanism for `invariant_enforced` decisions supports two operations: