feat(infospace,llm): agent ergonomics — entity lookup, model fallback, better errors

- `markitect infospace entity <name>`: single-entity lookup tolerating
  hyphens/underscores/case, with substring matching, ambiguity listing,
  and near-match hints. Prints slug, source path, domain, chapter, word
  count, VSM system, overall score, evaluator, and evaluation file path.
- `markitect infospace evaluate --model-fallback <model>`: if any
  entities fail with a rate-limit error, retry just those with a fresh
  adapter on the fallback model (different free-tier models have
  separate quota buckets).
- `markitect llm-check`: advisory when `OPENROUTER_API_KEY` is set but
  not used by the resolved provider; targeted hint when OpenRouter
  returns 401 (almost always a stale env key).
- `build_state`: raises `TypeError` with actionable message if passed a
  path instead of an `InfospaceConfig` — prior failure mode was a
  confusing `AttributeError` deep in the stack.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

markitect/helper/cli.py

@@ -240,8 +240,14 @@ def llm_catalog(output_format):
 )
 def llm_check(provider, model):
     """Send a minimal prompt to verify a provider is reachable and responding."""
+    import os
+
     from markitect.llm import create_adapter
-    from markitect.llm.exceptions import LLMConfigurationError, LLMError
+    from markitect.llm.exceptions import (
+        LLMAPIError,
+        LLMConfigurationError,
+        LLMError,
+    )
     from markitect.prompts.execution.models import RunConfig
 
     resolved = resolve_llm(cli_provider=provider, cli_model=model)
@@ -252,6 +258,17 @@ def llm_check(provider, model):
         f"  model from:    {resolved.model_source}"
     )
 
+    # Advisory: OPENROUTER_API_KEY is set but this call won't use it. Common
+    # source of "works for me, fails for agents" when the env var holds a
+    # stale key that overrides a clean config entry.
+    if resolved.provider != "openrouter" and os.environ.get("OPENROUTER_API_KEY"):
+        click.echo(
+            "  note: OPENROUTER_API_KEY is set but won't be used for this "
+            "provider. If OpenRouter calls fail elsewhere with 401, the env "
+            "var may be stale — unset or update it.",
+            err=True,
+        )
+
     try:
         adapter = create_adapter(
             provider=resolved.provider,
@@ -273,6 +290,19 @@ def llm_check(provider, model):
     except LLMError as exc:
         elapsed = time.monotonic() - start
         click.echo(f"ERROR \u2014 LLM error after {elapsed:.1f}s: {exc}", err=True)
+        # Targeted hint: 401 on openrouter almost always means a stale key.
+        if (
+            resolved.provider == "openrouter"
+            and isinstance(exc, LLMAPIError)
+            and exc.status_code == 401
+        ):
+            click.echo(
+                "  hint: OpenRouter returned 401 (unauthorized). Check whether "
+                "OPENROUTER_API_KEY is stale (`unset OPENROUTER_API_KEY` to "
+                "fall back to the key in ~/.config/markitect/config.toml, or "
+                "update the env var).",
+                err=True,
+            )
         sys.exit(1)
     except Exception as exc:
         elapsed = time.monotonic() - start