fix(intercept): name the sessionId namespace in ledger deny hints

[LanNguyenSi]

What

Ledger-gate deny "to satisfy" hints now name the sessionId namespace the unblocking ledger entry must be written under.

before: ... To satisfy: record an evidence-ledger entry containing `review:42` (session `sess-1`).
after:  ... To satisfy: record an evidence-ledger entry containing `review:42`, under this runtime session's id `sess-1` (not the agent-tasks task UUID).

Why

Two ledger namespaces exist: the runtime session id (harness runtime MCP gates) and the agent-tasks task UUID (the CI merge-approval GitHub Check). The deny hint showed the session id value but never named which namespace it was, so an agent holding both a session id and a task UUID could write under the wrong one. An entry under the task UUID never satisfies a harness runtime gate, which reads, writes, and hints under the same resolveSessionId value. This caused a real production failure (2026-05-17, PRs #174/#175): the first write under the task UUID was rejected, the second under the session id passed.

How

• src/runtime/intercept.ts: the hintSuffix now names the namespace identity. Naming an identity is not a producer verb, so the deny path stays neutral on producer choice (agent-tasks/88ca4bb3); the recordHint contract in src/policies/requires.ts is unchanged.
• The ux: agent-facing path and the sibling understanding-gate denies are out of scope (different surface, and no task-UUID ambiguity there).

Tests / verification

• New mutation-checked test asserts both the required tag and the namespace clause are present (drop the clause and it goes red).
• The two exact-string deny tests are updated.
• tsc clean; full vitest 2468 passed / 1 skipped; integration 1 passed; ug-schema-drift OK.

Review

Independent reviewer subagent: APPROVE (accept_with_notes), no high or critical findings. The one in-scope low finding (missing CHANGELOG entry) is addressed; the wording nit is applied.

Refs: discovery-2026-06-24/ledger-deny-namespace-hint (cdc60d56)