feat: de-risk agent loop — semantic tool schema + agent loop + real-WP spike harness

- api/agents: tool-schemas (semantic allowlist), agent-loop (multi-step + budget), circuit-breaker, llm-client/tool-executor interfaces
- api/agents: WpRestExecutor (real WP REST), OpenRouterLlmClient
- e2e/agent: multi-step prompts + run-agent-spike runner (scores rendered changes)
- ADR 0017; 101 unit tests green

docs/decisions/0017-semantic-tool-schema.md

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+# 17. The agent is given a semantic, allowlisted tool schema — not a raw wp_cli surface
+
+- **Status:** Accepted
+- **Date:** 2026-08-15
+
+## Context
+
+IMPLEMENTATION's Sprint 3 sketch exposed a single `wp_cli` tool and tested that `wp eval` / `wp config` / `DROP TABLE` / `wp plugin install http` never appear in the schema. The product is a general-purpose coding agent ("type anything, the agent does it"), which needs richer tools, and the safety guarantee is better served by *not exposing* a raw shell-like surface at all.
+
+## Decision
+
+The agent's tool schema is a set of **semantic, allowlisted tools** — `read_page`, `update_post`, `update_option`, `create_page`, `update_theme_json` — each mapping to a constrained WordPress operation. There is no `wp_cli`, `eval`, `config`, or raw SQL tool.
+
+### Options considered
+
+- Raw `wp_cli` tool with a deny-list of subcommands.
+- Semantic allowlisted tools (chosen).
+
+### Rejected
+
+- Raw `wp_cli` — a deny-list is fail-open by nature; a new dangerous subcommand is one miss away. An allowlist of semantic tools is fail-closed.
+
+## Consequences
+
+- `api/src/agents/tool-schemas.ts` is the single allowlist; new capability is a new semantic tool with its own executor mapping, reviewed on its own.
+- This is the tool surface the real-WP spike (`e2e/agent/`) exercises.