Tasks: the stop gate blocks on a node the work item never entered

Phase 4 of 4. Each task names the requirement it satisfies and the testing-plan row that proves it.

Task list

[x] A0: reproduce. The bugfix's console session on main at 48cb8e6: check says phase-selection, and the gate exits 2 demanding design.md. Req: all · Test: T8.
[x] A1: pointer on the report. StatusReport.pointer from state.current_node, emitted by as_dict. Req: R3.1, R3.2, R3.4 · Test: T3.
[x] A2: the gate walks to the pointer. blocking_node: inconclusive without a resolvable currentNode or pointer; the first unsatisfied node at or before the pointer, if block; currentNode as the bound when there is no pointer key. The run_check docstring is restated. Deps: A1 · Req: R1, R2 · Test: T1, T2, T4, T6.
[x] A3: the table says both. _state_line names the pointer under --recompute when it differs. Deps: A1 · Req: R3.3 · Test: T5.
[x] A4: tests. New cases in test_harness_gate.py; the new module test_gate_pointer_integration.py; the key pin in test_core_graphs.py. Deps: A1–A3 · Test: T1–T7.
[x] B1: interface docs. POST /graph/check's description (route and OpenAPI contract), the check_work_item MCP tool. Deps: A1 · Test: T11.
[x] C1: capability and CLI docs. docs/capabilities/process-graph.md gets the requirement and a history row; docs/capabilities/cli.md, docs/cli/commands/check.md and skills/the-loop/reference/automation.md are updated. Deps: A2, A3 · Test: T10.
[x] D1: evidence. verification.md, self-review.md, security-review.md, documentation.md, reviewer-briefing.md. Deps: A0–C1.