Server overhaul: one test harness in tests/common for every test binary

core_api/common.rs becomes tests/common/mod.rs and sync_api/m4.rs tests/common/sync_fixtures.rs; each binary
includes them through #[path] (the binaries of SPEC §14.7 stay as they are). TempDir's Default moves into the
harness instead of three copies; the skeleton helpers take ids, tokens and TempDir from it. Milestone wording in
test docs and the server README replaced by what the code does; README seams and test layout updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

server/crates/kvitt-server/tests/skeleton/main.rs

@@ -1,5 +1,8 @@
-//! Integration tests of the M2a server skeleton: migration identity and pragmas, routes, authentication and the
-//! protocol rule, error shapes, and the wire types against `contracts/examples/`.
+//! Base server tests: migration identity and pragmas, routes, authentication and the protocol rule, error shapes,
+//! and the wire types against `contracts/examples/`.
+
+#[path = "../common/mod.rs"]
+pub mod common;
 
 mod errors;
 mod migration;

server/crates/kvitt-server/tests/skeleton/routes.rs

@@ -80,7 +80,7 @@ async fn every_route_is_registered_and_implemented() {
         33,
         "SPEC §7 has 33 operations"
     );
-    // M3 implemented E-3 to E-30 and E-33 (tests/core_api), M4 the sync routes (tests/sync_api): nothing is 501.
+    // Every route has its handler (behaviour in tests/core_api and tests/sync_api): nothing is 501.
     for (method, path, _) in routes {
         let reply = app
             .send(authed(method.clone(), &path, &admin_token()))

server/crates/kvitt-server/tests/skeleton/support.rs

@@ -1,7 +1,7 @@
-//! Shared helpers of the skeleton tests: a migrated temporary database, seeded users and devices, a fixed
-//! clock and a one-shot request helper.
+//! Helpers of the base tests: a database migrated to a chosen schema version, seeded users and devices (the
+//! revoked device here is the member's), a fixed clock and a one-shot request helper. Ids, tokens and the
+//! temporary directory come from the shared harness (`tests/common/`).
 
-use std::path::PathBuf;
 use std::sync::Arc;
 
 use axum::body::Body;
@@ -12,45 +12,14 @@ use kvitt_server::time::{FixedClock, parse_ts};
 use kvitt_server::{AppState, auth, db, router};
 use serde_json::Value;
 use tower::ServiceExt;
-use uuid::Uuid;
 
-pub const ADMIN_ID: &str = "0192a000-0000-7000-8000-000000000001";
-pub const MEMBER_ID: &str = "0192a000-0000-7000-8000-000000000002";
-pub const ADMIN_DEVICE_ID: &str = "0192a001-0000-7000-8000-000000000001";
-pub const MEMBER_DEVICE_ID: &str = "0192a001-0000-7000-8000-000000000002";
-pub const REVOKED_DEVICE_ID: &str = "0192a001-0000-7000-8000-000000000003";
-pub const NOW: &str = "2026-10-17T12:00:00.000Z";
+pub use crate::common::{
+    ADMIN_DEVICE_ID, ADMIN_ID, MEMBER_DEVICE_ID, MEMBER_ID, NOW, TempDir, admin_token,
+    member_token, old_device_token as revoked_token, token,
+};
 
-pub fn token(tag: char) -> String {
-    format!("kvt_{}", tag.to_string().repeat(43))
-}
-
-pub fn admin_token() -> String {
-    token('A')
-}
-pub fn member_token() -> String {
-    token('M')
-}
-pub fn revoked_token() -> String {
-    token('R')
-}
-
-/// A data directory removed on drop.
-pub struct TempDir(pub PathBuf);
-
-impl TempDir {
-    pub fn new() -> Self {
-        let dir = std::env::temp_dir().join(format!("kvitt-test-{}", Uuid::now_v7()));
-        std::fs::create_dir_all(&dir).unwrap();
-        Self(dir)
-    }
-}
-
-impl Drop for TempDir {
-    fn drop(&mut self) {
-        let _ = std::fs::remove_dir_all(&self.0);
-    }
-}
+/// The member's revoked device (the id of the shared harness's old admin device).
+pub const REVOKED_DEVICE_ID: &str = crate::common::ADMIN_OLD_DEVICE_ID;
 
 pub struct TestApp {
     /// Kept alive so the directory is removed when the app is dropped.

server/crates/kvitt-server/tests/skeleton/wire_examples.rs

@@ -103,7 +103,7 @@ fn every_example_round_trips() {
                 round_trip::<ErrorBody>(&name, &example);
                 checked += 1;
             } else if dir_name == "push" {
-                // FCM payloads (SPEC §14.6) are built by M4's sender, not by a wire type of this crate.
+                // FCM payloads (SPEC §14.6) are built by the push sender, not by a wire type of this crate.
                 continue;
             } else if check(&name, &example) {
                 checked += 1;