recon + sqlglot validator + drill_down package; guard ReAct dimension picks against candidate list

api/prompts/planner.system.txt

@@ -6,7 +6,16 @@ Output: a JSON object with exactly this shape, in one fenced ```json block:
 {
   "rationale": "<one sentence on why this plan>",
   "steps": [
-    {"analysis": "<analysis_name>", "args": { ... }, "why": "<one sentence>"}
+    {
+      "analysis": "<analysis_name>",
+      "args": { ... },
+      "why": "<one sentence>",
+      "fallback": {                          // OPTIONAL — see rules
+        "analysis": "<analysis_name>",
+        "args": { ... },
+        "why": "<one sentence>"
+      }
+    }
   ]
 }
 
@@ -15,3 +24,4 @@ Rules:
 - The `args` keys must match the analysis's args_schema; additional keys are ignored, missing optional ones are fine.
 - Most questions are single-step. Only chain analyses when the second genuinely needs the first's output.
 - Comparing two periods is ONE `compare_periods` step, not two `direct_answer` steps.
+- A step's `fallback` is optional. Include one when the primary analysis is speculative (e.g. an exploratory `drill_down` that might find nothing useful) and there's a safer Analysis that can still produce an answer. The fallback runs only if the primary errors or yields no finding. Fallbacks must not themselves have fallbacks.