Bug Description

When HERMES_LANGFUSE_PUBLIC_KEY is set to a placeholder value (e.g., "placeholder" or "test-key"), the Langfuse SDK plugin successfully registers its hooks but never emits any traces to Langfuse. The failure is completely silent — no errors are logged, no warnings are shown, and the plugin appears to be functioning normally.

Steps to Reproduce

1. Set HERMES_LANGFUSE_PUBLIC_KEY to a placeholder value (e.g., "placeholder")
2. Set HERMES_LANGFUSE_SECRET_KEY to a placeholder value (e.g., "placeholder")
3. Set HERMES_LANGFUSE_HOST to a valid Langfuse instance URL
4. Run Hermes Agent with the Langfuse plugin enabled
5. Observe that no traces appear in Langfuse
6. Check logs — no errors or warnings related to Langfuse are present

Expected Behavior

The plugin should either:

• Validate the API key format and reject placeholder values at startup with a clear error message
• Emit a warning when trace submission fails due to invalid credentials
• Fail fast and disable the plugin if credentials are invalid

Actual Behavior

The plugin registers hooks successfully but silently fails to emit traces. No errors or warnings are logged, making it difficult to diagnose why observability is missing.

Environment

• Hermes Agent version: latest
• Langfuse SDK plugin: enabled
• HERMES_LANGFUSE_PUBLIC_KEY: placeholder value
• HERMES_LANGFUSE_SECRET_KEY: placeholder value
• HERMES_LANGFUSE_HOST: valid URL