Add compare command to diff two agents' results side by side (#49)

- `thinktank compare 1 3` shows detailed comparison
- Displays: agent summaries, Jaccard similarity score with bar chart,
  file overlap (both/only-A/only-B), added line breakdown
- Uses existing diff-parser infrastructure for analysis

Closes #29

Co-authored-by: unknown <that-github-user@github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

src/cli.ts

@@ -2,6 +2,7 @@
 
 import { Command } from "commander";
 import { apply } from "./commands/apply.js";
+import { compare } from "./commands/compare.js";
 import { list } from "./commands/list.js";
 import { run } from "./commands/run.js";
 
@@ -65,6 +66,16 @@ program
     });
   });
 
+program
+  .command("compare <agentA> <agentB>")
+  .description("Compare two agents' results side by side")
+  .action(async (agentA: string, agentB: string) => {
+    await compare({
+      agentA: parseInt(agentA, 10),
+      agentB: parseInt(agentB, 10),
+    });
+  });
+
 program
   .command("list")
   .description("List results from the most recent ensemble run")

src/commands/compare.ts

@@ -0,0 +1,103 @@
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import pc from "picocolors";
+import { diffSimilarity, parseDiff } from "../scoring/diff-parser.js";
+import type { AgentResult, EnsembleResult } from "../types.js";
+
+export interface CompareOptions {
+  agentA: number;
+  agentB: number;
+}
+
+export async function compare(opts: CompareOptions): Promise<void> {
+  let result: EnsembleResult;
+  try {
+    const raw = await readFile(join(".thinktank", "latest.json"), "utf-8");
+    result = JSON.parse(raw);
+  } catch {
+    console.error("  No results found. Run `thinktank run` first.");
+    process.exit(1);
+  }
+
+  const agentA = result.agents.find((a) => a.id === opts.agentA);
+  const agentB = result.agents.find((a) => a.id === opts.agentB);
+
+  if (!agentA) {
+    console.error(`  Agent #${opts.agentA} not found.`);
+    console.error(`  Available: ${result.agents.map((a) => `#${a.id}`).join(", ")}`);
+    process.exit(1);
+  }
+  if (!agentB) {
+    console.error(`  Agent #${opts.agentB} not found.`);
+    console.error(`  Available: ${result.agents.map((a) => `#${a.id}`).join(", ")}`);
+    process.exit(1);
+  }
+
+  console.log();
+  console.log(pc.bold(`  Comparing Agent #${opts.agentA} vs Agent #${opts.agentB}`));
+  console.log(pc.dim("  " + "─".repeat(58)));
+  console.log();
+
+  // Summary table
+  printAgentSummary(agentA, result);
+  printAgentSummary(agentB, result);
+  console.log();
+
+  // Similarity score
+  const sim = diffSimilarity(agentA.diff, agentB.diff);
+  const pct = Math.round(sim * 100);
+  const bar = "█".repeat(Math.round(pct / 5)) + "░".repeat(20 - Math.round(pct / 5));
+  console.log(`  Similarity: ${bar} ${pct}%`);
+  console.log();
+
+  // File comparison
+  const filesA = new Set(agentA.filesChanged);
+  const filesB = new Set(agentB.filesChanged);
+  const allFiles = new Set([...filesA, ...filesB]);
+
+  console.log(pc.bold("  Files changed:"));
+  for (const file of [...allFiles].sort()) {
+    const inA = filesA.has(file);
+    const inB = filesB.has(file);
+    if (inA && inB) {
+      console.log(`    ${pc.green("both")}  ${file}`);
+    } else if (inA) {
+      console.log(`    ${pc.cyan(`#${opts.agentA} only`)}  ${file}`);
+    } else {
+      console.log(`    ${pc.yellow(`#${opts.agentB} only`)}  ${file}`);
+    }
+  }
+  console.log();
+
+  // Unique lines comparison
+  const parsedA = parseDiff(agentA.diff);
+  const parsedB = parseDiff(agentB.diff);
+  const linesA = new Set(parsedA.flatMap((f) => f.addedLines.map((l) => `${f.path}:${l.trim()}`)));
+  const linesB = new Set(parsedB.flatMap((f) => f.addedLines.map((l) => `${f.path}:${l.trim()}`)));
+
+  let shared = 0;
+  let onlyA = 0;
+  let onlyB = 0;
+  for (const line of linesA) {
+    if (linesB.has(line)) shared++;
+    else onlyA++;
+  }
+  for (const line of linesB) {
+    if (!linesA.has(line)) onlyB++;
+  }
+
+  console.log(pc.bold("  Added lines:"));
+  console.log(`    Shared:        ${shared}`);
+  console.log(`    Only #${opts.agentA}:      ${onlyA}`);
+  console.log(`    Only #${opts.agentB}:      ${onlyB}`);
+  console.log();
+}
+
+function printAgentSummary(agent: AgentResult, result: EnsembleResult): void {
+  const test = result.tests.find((t) => t.agentId === agent.id);
+  const testStr = test ? (test.passed ? pc.green("pass") : pc.red("fail")) : pc.dim("n/a");
+  const rec = result.recommended === agent.id ? pc.cyan(" (recommended)") : "";
+  console.log(
+    `  Agent #${agent.id}${rec}: ${agent.status} | tests: ${testStr} | +${agent.linesAdded}/-${agent.linesRemoved} | ${agent.filesChanged.length} files`,
+  );
+}