What causes "Failed to store MCP token for '{}': {}" in Kuberwastaken/claurst?

Inspect the inner error text to see the underlying storage failure

Kuberwastaken/claurst · error · anyhow::Error

Failed to store MCP token for

Error message

Failed to store MCP token for '{}': {}

What it means

After a successful OAuth flow completes, the resulting token is persisted via oauth::store_mcp_token. If persistence fails (I/O error, storage backend unavailable), the original error is wrapped with this message naming the server. The token may still be valid in memory but was not saved, so it will not survive the session.

Solutions

Inspect the inner error text to see the underlying storage failure
Check that the token/config directory exists and is writable by the process
Re-run the auth flow once the storage issue is fixed — the token is not persisted
Free disk space / resolve file locks if the store could not be written

Defensive patterns

Strategy: try-catch

Validate before calling

let dir = token_store_dir()?;
let probe = dir.join(".write-probe");
std::fs::write(&probe, b"ok").context("token store dir not writable")?;
let _ = std::fs::remove_file(&probe);

Try / catch

match oauth::store_mcp_token(&token) {
    Ok(()) => {}
    Err(e) => {
        eprintln!("warning: token for {server} not persisted: {e}; re-auth next session");
    }
}

Prevention

Ensure the config/token directory exists and is writable before starting auth
Avoid running multiple auth flows concurrently against the same store
Monitor free disk space on hosts running the auth flow
On failure, re-run authentication before relying on the token later

When it happens

Trigger: run_mcp_auth_flow() finished the browser flow but store_mcp_token(&mcp_token) returned Err — disk full, auth-store file locked/unwritable, storage directory missing, or serialization failure.

Common situations: Home directory or config dir not writable (sandboxed process, read-only FS); concurrent runs of the auth flow corrupting/locking the token store; disk quota exceeded; corrupted auth store file forcing rewrite failure.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

AI-assisted analysis of Kuberwastaken/claurst@b0637c97ec (2026-09-10). Data as JSON: /api/errors/9dc6cb9cb020c3d4. Report an issue: GitHub.

Appendix: source

Thrown at src-rust/crates/mcp/src/lib.rs:1281

        token: &str,
        expires_in: Option<u64>,
    ) -> anyhow::Result<()> {
        let expires_at = expires_in.map(|secs| {
            std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs()
                + secs
        });
        let mcp_token = oauth::McpToken {
            access_token: token.to_string(),
            refresh_token: None,
            expires_at,
            scope: None,
            server_name: server_name.to_string(),
        };
        oauth::store_mcp_token(&mcp_token)
            .map_err(|e| anyhow::anyhow!("Failed to store MCP token for '{}': {}", server_name, e))
    }

    /// Load the stored OAuth access token for an MCP server, if any.
    ///
    /// Returns `None` if no token is stored or the token cannot be refreshed.
    pub async fn load_token(&self, server_name: &str) -> Option<String> {
        let config = self.server_configs.get(server_name)?;
        let server_url = config.url.as_deref()?;
        oauth::get_valid_mcp_access_token(server_name, server_url)
            .await
            .ok()
            .flatten()
    }

    // -----------------------------------------------------------------------
    // Notification dispatch loop
    // -----------------------------------------------------------------------

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