diff --git a/src/config.ts b/src/config.ts
index 46ce910..f816378 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -1,9 +1,43 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 // Copyright (C) 2026 Giancarlo Erra - Altaire Limited
+import { execFileSync } from "node:child_process";
 import { createHash } from "node:crypto";
 import fs from "node:fs";
 import path from "node:path";
 
+// ── Branch detection ─────────────────────────────────────────────────────
+
+/**
+ * Detect the current git branch for a project path.
+ * Returns `null` if the path is not inside a git repository or detection fails.
+ */
+export function detectGitBranch(projectPath: string): string | null {
+  try {
+    const branch = execFileSync("git", ["rev-parse", "--abbrev-ref", "HEAD"], {
+      cwd: path.resolve(projectPath),
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    }).trim();
+    // "HEAD" is returned for detached HEAD state — treat as no branch
+    return branch && branch !== "HEAD" ? branch : null;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Sanitize a git branch name for use in Qdrant collection names.
+ * Replaces characters outside `[a-zA-Z0-9_-]` with underscores,
+ * collapses consecutive underscores, and strips leading/trailing underscores.
+ */
+export function sanitizeBranchName(branch: string): string {
+  return branch
+    .replace(/[^a-zA-Z0-9_-]/g, "_")
+    .replace(/_+/g, "_")
+    .replace(/^_|_$/g, "");
+}
+
 /**
  * Generate a stable project ID from an absolute folder path.
  * Uses a short SHA-256 prefix so collection names stay Qdrant-friendly.
@@ -12,6 +46,10 @@ import path from "node:path";
  * of hashing the path.  This lets multiple directory trees (e.g. git
  * worktrees) share a single Qdrant index.  The value must contain only
  * characters valid in a Qdrant collection name (`[a-zA-Z0-9_-]`).
+ *
+ * When `SOCRATICODE_BRANCH_AWARE` is `"true"` (and no explicit project ID
+ * is set), the current git branch name is appended to the hash, producing
+ * a separate set of collections per branch.
  */
 export function projectIdFromPath(folderPath: string): string {
   const explicit = process.env.SOCRATICODE_PROJECT_ID?.trim();
@@ -24,7 +62,17 @@ export function projectIdFromPath(folderPath: string): string {
     return explicit;
   }
   const normalized = path.resolve(folderPath);
-  return createHash("sha256").update(normalized).digest("hex").slice(0, 12);
+  let id = createHash("sha256").update(normalized).digest("hex").slice(0, 12);
+
+  // Branch-aware mode: append sanitized branch name to isolate per-branch indexes
+  if (process.env.SOCRATICODE_BRANCH_AWARE === "true") {
+    const branch = detectGitBranch(normalized);
+    if (branch) {
+      id = `${id}__${sanitizeBranchName(branch)}`;
+    }
+  }
+
+  return id;
 }
 
 /**
diff --git a/tests/unit/config.test.ts b/tests/unit/config.test.ts
index 4465169..bbecb3a 100644
--- a/tests/unit/config.test.ts
+++ b/tests/unit/config.test.ts
@@ -4,17 +4,23 @@ import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
-import { collectionName, contextCollectionName, graphCollectionName, loadLinkedProjects, projectIdFromPath, resolveLinkedCollections } from "../../src/config.js";
+import { collectionName, contextCollectionName, detectGitBranch, graphCollectionName, loadLinkedProjects, projectIdFromPath, resolveLinkedCollections, sanitizeBranchName } from "../../src/config.js";
 
 describe("config", () => {
-  // Clean up env override between tests
+  // Clean up env overrides between tests
   const originalEnv = process.env.SOCRATICODE_PROJECT_ID;
+  const originalBranchAware = process.env.SOCRATICODE_BRANCH_AWARE;
   afterEach(() => {
     if (originalEnv === undefined) {
       delete process.env.SOCRATICODE_PROJECT_ID;
     } else {
       process.env.SOCRATICODE_PROJECT_ID = originalEnv;
     }
+    if (originalBranchAware === undefined) {
+      delete process.env.SOCRATICODE_BRANCH_AWARE;
+    } else {
+      process.env.SOCRATICODE_BRANCH_AWARE = originalBranchAware;
+    }
   });
 
   describe("projectIdFromPath", () => {
@@ -277,4 +283,99 @@ describe("config", () => {
       expect(collections[0].name).not.toBe(collections[1].name);
     });
   });
+
+  // ── Branch awareness ────────────────────────────────────────────────
+
+  describe("sanitizeBranchName", () => {
+    it("passes through simple branch names", () => {
+      expect(sanitizeBranchName("main")).toBe("main");
+      expect(sanitizeBranchName("develop")).toBe("develop");
+    });
+
+    it("replaces slashes with underscores", () => {
+      expect(sanitizeBranchName("feat/my-feature")).toBe("feat_my-feature");
+    });
+
+    it("handles deeply nested branch names", () => {
+      expect(sanitizeBranchName("feature/JIRA-123/some-work")).toBe(
+        "feature_JIRA-123_some-work",
+      );
+    });
+
+    it("collapses consecutive underscores", () => {
+      expect(sanitizeBranchName("feat//double")).toBe("feat_double");
+    });
+
+    it("strips leading and trailing underscores", () => {
+      expect(sanitizeBranchName("/leading")).toBe("leading");
+      expect(sanitizeBranchName("trailing/")).toBe("trailing");
+    });
+
+    it("preserves hyphens", () => {
+      expect(sanitizeBranchName("my-branch-name")).toBe("my-branch-name");
+    });
+
+    it("replaces special characters", () => {
+      expect(sanitizeBranchName("feat@v2.0")).toBe("feat_v2_0");
+    });
+  });
+
+  describe("detectGitBranch", () => {
+    it("detects a branch in the current repo", () => {
+      // This test runs inside the socraticode git repo
+      const branch = detectGitBranch(process.cwd());
+      expect(branch).toBeTruthy();
+      expect(typeof branch).toBe("string");
+    });
+
+    it("returns null for non-git directories", () => {
+      const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "socraticode-nogit-"));
+      try {
+        expect(detectGitBranch(tmpDir)).toBeNull();
+      } finally {
+        fs.rmSync(tmpDir, { recursive: true, force: true });
+      }
+    });
+  });
+
+  describe("projectIdFromPath with SOCRATICODE_BRANCH_AWARE", () => {
+    it("does not include branch suffix by default", () => {
+      const id = projectIdFromPath("/some/project/path");
+      expect(id).toMatch(/^[0-9a-f]{12}$/);
+      expect(id).not.toContain("__");
+    });
+
+    it("appends branch suffix when SOCRATICODE_BRANCH_AWARE=true", () => {
+      process.env.SOCRATICODE_BRANCH_AWARE = "true";
+      // Run from current repo directory so git detection works
+      const id = projectIdFromPath(process.cwd());
+      expect(id).toContain("__");
+      // Hash part + __ + branch
+      const parts = id.split("__");
+      expect(parts[0]).toMatch(/^[0-9a-f]{12}$/);
+      expect(parts[1]).toBeTruthy();
+    });
+
+    it("produces valid Qdrant collection names with branch suffix", () => {
+      process.env.SOCRATICODE_BRANCH_AWARE = "true";
+      const id = projectIdFromPath(process.cwd());
+      const coll = collectionName(id);
+      // Must be valid Qdrant name: [a-zA-Z0-9_-]+
+      expect(coll).toMatch(/^[a-zA-Z0-9_-]+$/);
+    });
+
+    it("does not append branch when SOCRATICODE_PROJECT_ID is set", () => {
+      process.env.SOCRATICODE_BRANCH_AWARE = "true";
+      process.env.SOCRATICODE_PROJECT_ID = "explicit-id";
+      const id = projectIdFromPath(process.cwd());
+      expect(id).toBe("explicit-id");
+      expect(id).not.toContain("__");
+    });
+
+    it("does not append branch when SOCRATICODE_BRANCH_AWARE is not true", () => {
+      process.env.SOCRATICODE_BRANCH_AWARE = "false";
+      const id = projectIdFromPath(process.cwd());
+      expect(id).toMatch(/^[0-9a-f]{12}$/);
+    });
+  });
 });