Create Claude Plugin (#5672)

**Based on: #5582

# Description of Changes

Add a Claude plugin for the SpacetimeDB skills and MCP server, alongside
the existing Codex plugin. The entry uses `strict: false`, so it reads
`skills/` directly and declares the MCP server inline. Usage:

```bash
claude plugin marketplace add clockworklabs/SpacetimeDB
claude plugin install spacetimedb@spacetimedb-plugins
```

<!-- Please describe your change, mention any related tickets, and so on
here. -->

# API and ABI breaking changes
None.

<!-- If this is an API or ABI breaking change, please apply the
corresponding GitHub label. -->

# Expected complexity level and risk
1

<!--
How complicated do you think these changes are? Grade on a scale from 1
to 5,
where 1 is a trivial change, and 5 is a deep-reaching and complex
change.

This complexity rating applies not only to the complexity apparent in
the diff,
but also to its interactions with existing and future code.

If you answered more than a 2, explain what is complex about the PR,
and what other components it interacts with in potentially concerning
ways. -->

# Testing

<!-- Describe any testing you've done, and any testing you'd like your
reviewers to do,
so that you're confident that all the changes work as expected! -->

- [x] I tested the Claude plugin, `claude plugin validate .` passes,
then install and `claude plugin details spacetimedb` reports the skills
and MCP server.

For testing, from repo root:

```bash
claude plugin validate .
claude plugin marketplace add ./
claude plugin install spacetimedb@spacetimedb-plugins
claude plugin details spacetimedb
```

Then restart Claude

Author: clockwork-tien

.agents/plugins/marketplace.json

@@ -0,0 +1,20 @@
+{
+  "name": "spacetimedb-plugins",
+  "interface": {
+    "displayName": "SpacetimeDB"
+  },
+  "plugins": [
+    {
+      "name": "spacetimedb",
+      "source": {
+        "source": "local",
+        "path": "./codex-plugin/plugins/spacetimedb"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_USE"
+      },
+      "category": "Developer Tools"
+    }
+  ]
+}

.claude-plugin/README.md

@@ -0,0 +1,20 @@
+# SpacetimeDB for Claude Code
+
+`marketplace.json` here installs the repository's `skills/` directory and the SpacetimeDB MCP
+server into Claude Code:
+
+```bash
+claude plugin marketplace add clockworklabs/SpacetimeDB
+claude plugin install spacetimedb@spacetimedb-plugins
+```
+
+From a local checkout, use `./` as the source. Confirm with `claude plugin details spacetimedb`,
+which lists the skills and the MCP server. The MCP server runs `spacetime mcp`, which bridges
+stdio to the HTTP endpoint on whichever server your CLI is configured for.
+
+## Maintaining
+
+The entry uses `strict: false`, so it reads `skills/` directly and needs no manifest inside a
+plugin payload. It lists each skill explicitly, so adding one under `skills/` means adding it
+here too. `cargo ci lint` fails when the list and the directory disagree. Validate the catalog
+with `claude plugin validate .`.

.claude-plugin/marketplace.json

@@ -0,0 +1,42 @@
+{
+  "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
+  "name": "spacetimedb-plugins",
+  "description": "SpacetimeDB plugins for Claude Code",
+  "owner": {
+    "name": "Clockwork Labs",
+    "url": "https://spacetimedb.com"
+  },
+  "plugins": [
+    {
+      "name": "spacetimedb",
+      "displayName": "SpacetimeDB",
+      "description": "SpacetimeDB skills for building modules and clients in Rust, C#, TypeScript, C++, Unity, and Unreal, plus an MCP server that lists your databases, reads schemas, runs SQL, and calls reducers with your CLI login.",
+      "author": {
+        "name": "Clockwork Labs"
+      },
+      "category": "database",
+      "homepage": "https://spacetimedb.com",
+      "source": "./skills",
+      "strict": false,
+      "skills": [
+        "./cli",
+        "./concepts",
+        "./cpp-server",
+        "./csharp-client",
+        "./csharp-server",
+        "./mcp",
+        "./rust-server",
+        "./typescript-client",
+        "./typescript-server",
+        "./unity",
+        "./unreal"
+      ],
+      "mcpServers": {
+        "spacetimedb": {
+          "command": "spacetime",
+          "args": ["mcp"]
+        }
+      }
+    }
+  ]
+}

tools/ci/src/main.rs

@@ -359,6 +359,43 @@ fn check_codex_plugin_skills_sync() -> Result<()> {
     Ok(())
 }
 
+fn check_claude_marketplace_skills() -> Result<()> {
+    // Claude catalog lists each skill explicitly, so a new skill under `skills/` is
+    // invisible to Claude until it is added there
+    let catalog_path = Path::new(".claude-plugin/marketplace.json");
+    let contents = fs::read_to_string(catalog_path).with_context(|| format!("reading {}", catalog_path.display()))?;
+    let catalog: Value =
+        serde_json::from_str(&contents).with_context(|| format!("parsing {}", catalog_path.display()))?;
+    let listed: BTreeSet<String> = catalog["plugins"][0]["skills"]
+        .as_array()
+        .ok_or_else(|| anyhow::anyhow!("{} plugins[0].skills must be an array", catalog_path.display()))?
+        .iter()
+        .filter_map(|value| value.as_str())
+        .map(|entry| entry.trim_start_matches("./").to_owned())
+        .collect();
+
+    let mut present = BTreeSet::new();
+    for entry in fs::read_dir("skills").with_context(|| "reading skills")? {
+        let entry = entry?;
+        if entry.path().join("SKILL.md").is_file() {
+            present.insert(entry.file_name().to_string_lossy().into_owned());
+        }
+    }
+
+    if listed != present {
+        let missing: Vec<_> = present.difference(&listed).cloned().collect();
+        let extraneous: Vec<_> = listed.difference(&present).cloned().collect();
+        bail!(
+            "{} skills list does not match skills/:\n  missing: {:?}\n  extraneous: {:?}\nUpdate the skills list in {}",
+            catalog_path.display(),
+            missing,
+            extraneous,
+            catalog_path.display()
+        );
+    }
+    Ok(())
+}
+
 #[derive(Subcommand)]
 enum CiCmd {
     /// Runs tests
@@ -683,6 +720,7 @@ fn main() -> Result<()> {
             ensure_repo_root()?;
             check_pnpm_release_age_policy()?;
             check_codex_plugin_skills_sync()?;
+            check_claude_marketplace_skills()?;
             // `cargo fmt --all` only checks files that Cargo discovers through workspace/package targets.
             // However, we also keep Rust sources in a locations that are tracked but not part of our workspace,
             // so this approach properly catches all the files, where `cargo fmt` does not.