mcp: HTTP concurrency test; state-machine suite tolerates a contended disk

tests/http_concurrency.rs: six HTTP clients at once against one store
(main.rs serve_http shares it): every bare entry refused at threshold
0.00, every receipted one posted, each contested draft posted exactly
once, books verify and balance, a restart replays the same head.

spec_mcp.rs: the response timeout is 180 s (a mutation run's jobs
contend for a synced disk; the baseline timed out at 30 s), and
MCP_CASES sets the state machine's cases (just mutants-mcp uses 16).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

Cargo.lock

@@ -2873,6 +2873,7 @@ dependencies = [
  "pin-project-lite",
  "smallvec",
  "tokio",
+ "want",
 ]
 
 [[package]]
@@ -2881,13 +2882,22 @@ version = "0.1.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ddc03d96684f9226b8a787cdb71488417b53ab5ea8fdb1dac946cb9431cc8bff"
 dependencies = [
+ "base64 0.23.1",
  "bytes",
+ "futures-channel",
+ "futures-util",
  "http",
  "http-body",
+ "httparse",
  "hyper",
+ "ipnet",
+ "libc",
+ "percent-encoding",
  "pin-project-lite",
+ "socket2",
  "tokio",
  "tower-service",
+ "tracing",
 ]
 
 [[package]]
@@ -3226,6 +3236,12 @@ dependencies = [
  "hybrid-array",
 ]
 
+[[package]]
+name = "ipnet"
+version = "2.12.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "791930b43c0d5973160d90a8f3894509f2b273430f5c5c73b668636d0287c5c0"
+
 [[package]]
 name = "is-docker"
 version = "0.2.0"
@@ -5358,6 +5374,40 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "19b30a45b0cd0bcca8037f3d0dc3421eaf95327a17cad11964fb8179b4fc4832"
 
+[[package]]
+name = "reqwest"
+version = "0.13.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "16a1cfa75cc186dd73d5818e510e042e40927bccc9c236b061cea97e1eb08029"
+dependencies = [
+ "base64 0.23.1",
+ "bytes",
+ "futures-core",
+ "futures-util",
+ "http",
+ "http-body",
+ "http-body-util",
+ "hyper",
+ "hyper-util",
+ "js-sys",
+ "log",
+ "percent-encoding",
+ "pin-project-lite",
+ "serde",
+ "serde_json",
+ "sync_wrapper",
+ "tokio",
+ "tokio-util",
+ "tower",
+ "tower-http",
+ "tower-service",
+ "url",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "wasm-streams",
+ "web-sys",
+]
+
 [[package]]
 name = "resvg"
 version = "0.47.0"
@@ -5402,6 +5452,7 @@ dependencies = [
  "pastey",
  "pin-project-lite",
  "rand 0.10.3",
+ "reqwest",
  "rmcp-macros",
  "schemars",
  "serde",
@@ -6152,6 +6203,9 @@ name = "sync_wrapper"
 version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0bf256ce5efdfa370213c1dabab5935a12e49f2c58d15e9eac2870d3b4f27263"
+dependencies = [
+ "futures-core",
+]
 
 [[package]]
 name = "synstructure"
@@ -6510,6 +6564,24 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "tower-http"
+version = "0.6.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4cfcf7e2740e6fc6d4d688b4ef00650406bb94adf4731e43c096c3a19fe40840"
+dependencies = [
+ "bitflags 2.13.2",
+ "bytes",
+ "futures-util",
+ "http",
+ "http-body",
+ "pin-project-lite",
+ "tower",
+ "tower-layer",
+ "tower-service",
+ "url",
+]
+
 [[package]]
 name = "tower-layer"
 version = "0.3.3"
@@ -6554,6 +6626,12 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "try-lock"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e421abadd41a4225275504ea4d6566923418b7f05506fbc9c0fe86ba7396114b"
+
 [[package]]
 name = "ttf-parser"
 version = "0.25.1"
@@ -7301,6 +7379,15 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "want"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec4cdd0dd910afe868b7ef477227d8d538b46b3075031afee8a9f2acb0a2ed0b"
+dependencies = [
+ "try-lock",
+]
+
 [[package]]
 name = "wasi"
 version = "0.11.1+wasi-snapshot-preview1"
@@ -7373,6 +7460,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "wasm-streams"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d1ec4f6517c9e11ae630e200b2b65d193279042e28edd4a2cda233e46670bbb"
+dependencies = [
+ "futures-util",
+ "js-sys",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "web-sys",
+]
+
 [[package]]
 name = "wasmi"
 version = "1.1.0"