Enforce LIP-0008 ingress legitimacy in validation

[danvoulez]

Summary

Stacked on #1. Adds the enforcement half of LIP-0008: validation now refuses ingress that violates the constitutional tier × grammar matrix, refuses half-context, and refuses capability when no manifest accepts the declared ingress. Per-manifest rejection does not fail early.

This PR has one talent: enforce ingress legitimacy.
It does not become a policy engine, it does not wire dispatch, and it does not call any LLM.

What changed

file	change
src/validation.rs	+ ingress_tier/ingress_grammar on AdmissibilityContext + 3 new ValidationError variants + validate_ingress_context function + per-manifest ingress filter in validate_capability (no early fail)
src/planning_compiler.rs	+ 3 new arms in validation_error_to_runtime_failure (ingress-tagged reason codes); + ..Default::default() in ctx() test helper
src/plan_executor.rs	+ ..Default::default() in ctx() test helper
src/lib.rs	re-export validate_ingress_context
tests/tier_grammar_validation.rs	NEW 10 focused tests

The three Dan-approved adjustments are in

1. Half-context fails — IncompleteIngressContext rejects (Some, None) and (None, Some). Legacy (None, None) still passes.
2. No early-fail across manifests — validate_capability iterates all manifests; NoCapabilityForIngress only fires when none accepts the declared ingress.
3. No "Operational cannot Execute" — primitive × grammar policy is out of scope here; this PR enforces only ingress legitimacy.

Tests (10)

legacy_both_none_passes                                    ✓
incomplete_tier_only_fails                                 ✓
incomplete_grammar_only_fails                              ✓
mini_plus_strong_fails_constitutionally                    ✓ (TierGrammarIllegitimate)
operator_plus_strong_passes_constitutionally               ✓
manifest_restricts_tier_fails_when_no_alternative          ✓ (NoCapabilityForIngress)
manifest_restricts_grammar_fails_when_no_alternative       ✓ (NoCapabilityForIngress)
multi_manifest_one_accepts_passes                          ✓ (no early fail)
legacy_manifest_passes_when_context_declares_ingress       ✓ (manifest None = permissive)
manifest_explicitly_accepts_passes                         ✓

Lib regression: 141/141 passing, unchanged.

What this PR does NOT do (intentional)

• ✗ Doesn't wire operational_grammar.rs / strong_grammar.rs to set ingress_tier/ingress_grammar on the context. Caller responsibility; lands in spike PR 4.
• ✗ Doesn't modify admission.rs. Those types (Boundary/Gate/Passport/Visa) are unchanged; this PR works through the validation.rs pipeline.
• ✗ Doesn't implement entropy thresholds, Pocket Runtime, Tower/LAB integration, or any LLM call.
• ✗ Doesn't make Operational unable to lower Execute (primitive × grammar policy — separate PR if/when needed).

Gates

Gate 0 — governance review              LIP-0008 published (governance#2, Proposed)
Gate 1 — consistency pass               clean
Gate 2 — PR 1 (types)                   Draft (#1)
Gate 3 — PR 2 (this, enforcement)       Draft, stacked on PR 1
Gate 4 — Pocket Runtime crate           future (logline-foundation/engine)
Gate 5 — spike GOLDEN-004 end-to-end    future

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