CB-609: bridge_ack takes target, not ticket; mark MCP-Contract.md as historical

The instruction surface named a parameter the tool refuses. bridge_ack requires
target and msgId (BridgeMcp.java:1001) and errors with 'target and msgId are
required' otherwise, but step 5 of the primary procedure said bridge_ack{ticket,
msgId}. The table two sections below it was already correct, so the file
contradicted itself and the wrong half was in the numbered steps a lead follows.
The same line is fixed in the byte-identical wiki template.

docs/MCP-Contract.md still opened with 'Greenfield - no MCP code exists yet' and
CLAUDE.md pointed every session at it. Audited against BridgeMcp.java: it names
two tools that do not exist, omits four that do, gets nearly every parameter name
wrong, and uses /workers paths the daemon does not serve. Its status banner now
says so and names the live schema as the authority; CLAUDE.md's pointer is
narrowed to section 6, which is the part that did survive. Rewrite is CB-609.

docs/MCP-Contract.md

@@ -1,9 +1,24 @@
 # MCP Contract — `bridged`'s unified gateway
 
-> **Status:** 🟡 Design (2026-07-14). Greenfield — no MCP code exists yet; the pom carries
-> only Javalin/Jackson. This page defines the tool surface that CB-104 and its followers
-> implement. It supersedes nothing; it fills the "MCP server face" left open by the
-> [Architecture](1-Architecture) page.
+> **Status: 🔴 HISTORICAL DESIGN — do NOT use as the tool reference.** Written 2026-07-14, before
+> any MCP code existed. The system shipped and this page never caught up, so **its tool names,
+> parameter names and REST paths are wrong today**. Audited 2026-08-17; the specific drift:
+>
+> - **Tools it names that do not exist:** `bridge_read`, `bridge_cancel`.
+> - **Shipped tools it omits:** `bridge_poll`, `bridge_ack`, `bridge_profiles`, `bridge_whoami`.
+> - **Parameter names are wrong nearly everywhere** — it says `message`/`target`/`timeout_seconds`/
+>   `block` where the code takes `content`/`sessionId`/`timeoutMs`/`wait`; `text` where
+>   `bridge_reply` takes `content`; `target` where `bridge_stop` takes `paneId`.
+> - **REST paths are wrong:** it says `POST /workers` and `DELETE /workers/{paneId}`; the daemon
+>   serves `POST /members` and `DELETE /members/{paneId}`.
+>
+> **The authoritative tool surface is the live MCP schema** (each tool's own description and
+> parameters, as mounted), with the intent→tool table in `CLAUDE.md` as the short form. Both were
+> checked against `mcp/BridgeMcp.java` on 2026-08-17 and are accurate.
+>
+> What is still worth reading here is **§6 — the flows and the error model** (rendezvous,
+> `bridge_ask`, detached delivery, the turn-done fallback). The shapes it describes are the ones
+> that shipped; only the names around them drifted. Rewriting this page is tracked as **CB-609**.
 
 `bridged` is the **sole communication gateway** for every Claude session in the bridge. Both
 the **primary** (Opus, on subscription) and every **worker** (off-subscription Claude Code)