fix(model-routing): stop halving the indented code-block count (#3364)

countCodeBlocks() summed fenced blocks with Math.floor(indentedBlocks / 2),
but the indented-block regex already coalesces each contiguous run of
indented lines into a single match — so indentedBlocks is already the
block count. The divisor discarded half of it: a prompt with one indented
code block scored 0, silently dropping its lexical-complexity signal
(scorer.ts gates on codeBlockCount > 0) and able to nudge borderline
prompts one model tier too low.

Drop the /2 so indented blocks count 1:1, matching the fenced path. Adds
regression tests for one- and two-indented-block prompts; both fail on the
old code and pass on the fix. Existing fenced-block test is unaffected.

Constraint: sole consumer is the `codeBlockCount > 0` gate in scorer.ts
Rejected: rework the regex to match per indented line | regex is correct as-is, the divisor is the defect
Confidence: high
Scope-risk: narrow
Not-tested: prompts mixing fenced and indented blocks in one string

src/__tests__/model-routing.test.ts

@@ -62,6 +62,18 @@ describe('Signal Extraction', () => {
       expect(signals.codeBlockCount).toBe(2);
     });
 
+    it('should count a single indented code block', () => {
+      const prompt = 'Here is code:\n    const x = 1;\n    return x;\ndone';
+      const signals = extractLexicalSignals(prompt);
+      expect(signals.codeBlockCount).toBe(1);
+    });
+
+    it('should count two separate indented code blocks', () => {
+      const prompt = 'First:\n    const a = 1;\n\nSecond:\n    const b = 2;';
+      const signals = extractLexicalSignals(prompt);
+      expect(signals.codeBlockCount).toBe(2);
+    });
+
     it('should detect architecture keywords', () => {
       const signals = extractLexicalSignals('We need to refactor the architecture');
       expect(signals.hasArchitectureKeywords).toBe(true);

src/features/model-routing/signals.ts

@@ -107,8 +107,10 @@ function countFilePaths(prompt: string): number {
  */
 function countCodeBlocks(prompt: string): number {
   const fencedBlocks = (prompt.match(/```[\s\S]*?```/g) || []).length;
+  // The indented-block regex coalesces each contiguous run of indented lines
+  // into a single match, so `indentedBlocks` is already the block count.
   const indentedBlocks = (prompt.match(/(?:^|\n)(?:\s{4}|\t)[^\n]+(?:\n(?:\s{4}|\t)[^\n]+)*/g) || []).length;
-  return fencedBlocks + Math.floor(indentedBlocks / 2);
+  return fencedBlocks + indentedBlocks;
 }
 
 /**