fix: rewrite 'no LLM provider' stderr to stop the capability-constraint misread

PR #285 introduced the stderr warning "No --plan and no LLM provider
configured. Using deterministic fallback..." The 2026-04-19 Run 1
agent self-debug said it read that as "I don't have a key, I can't do
LLM stuff, I have to accept fallback" - which is the exact wrong
mental model. The word "provider" referred to the engine's INTERNAL
planner credentials, but the agent parsed it as "I need credentials
to plan at all."

Rewritten to say plainly: YOU are the reasoning model hosting this
skill (Claude Code, Codex, Hermes, Gemini, or any agent runtime);
YOU ARE the planner; you do not need an API key or credentials - you
ARE the LLM. The --plan flag exists precisely so a reasoning model
generates its own plan upstream and passes it to the engine. The
deterministic fallback is the headless/cron path only.

Runtime enumeration is explicit so agents on every supported runtime
recognize themselves - this skill ships to Claude Code, Codex, Hermes,
and ~/.agents via sync.sh.

Tests: updated test_fallback_logs_warning_when_no_provider to assert
the new language (YOU ARE the planner, runtime names present) and
assert the old misleading phrasing is absent. Renamed the companion
test for clarity.

tests/test_planner_v3.py

@@ -413,14 +413,24 @@ class FallbackDefaultsTests(unittest.TestCase):
                 provider=None,
                 model=None,
             )
-        self.assertIn("No --plan and no LLM provider configured", buf.getvalue())
+        output = buf.getvalue()
+        # New language: "No --plan passed" + "YOU ARE the planner" +
+        # runtime enumeration. Unit 4 (2026-04-19) rewrite to stop the
+        # "no provider = no LLM = I need a key" misread.
+        self.assertIn("No --plan passed", output)
+        self.assertIn("YOU ARE the planner", output)
+        self.assertIn("you ARE the LLM", output)
+        # Runtime-agnostic: each supported runtime name should appear.
+        for runtime_name in ("Claude Code", "Codex", "Hermes", "Gemini"):
+            self.assertIn(runtime_name, output)
+        # The old misleading phrasing must NOT appear.
+        self.assertNotIn("No --plan and no LLM provider configured", output)
 
-    def test_fallback_does_not_log_warning_when_provider_present(self):
+    def test_fallback_does_not_log_new_warning_when_provider_present(self):
         # When a provider is configured, the provider path runs; if it
-        # succeeds, no fallback warning should appear.
-        # (The existing sanitize tests cover this; we just confirm the
-        # warning string gating is on provider-presence, not on fallback
-        # activation.)
+        # errors, we get the "LLM planning failed" message, NOT the
+        # "No --plan passed" guidance (which is specifically for the
+        # no-provider-no-plan caller path).
         import io
         import contextlib
         buf = io.StringIO()
@@ -438,11 +448,9 @@ class FallbackDefaultsTests(unittest.TestCase):
                 provider=_NoopProvider(),
                 model="some-model",
             )
-        # Provider was present — we expect the "LLM planning failed" message,
-        # NOT the "No --plan and no LLM provider" message.
         output = buf.getvalue()
         self.assertIn("LLM planning failed", output)
-        self.assertNotIn("No --plan and no LLM provider configured", output)
+        self.assertNotIn("No --plan passed", output)
 
 
 if __name__ == "__main__":