feat: add fork functionality to create a copy of a run

main.py

@@ -1266,6 +1266,56 @@ async def delete_run(request: Request, run_id: str):
     return RedirectResponse(url=f"{BASE_PATH}/", status_code=303)
 
 
+@app.post("/d/{run_id}/fork", response_class=HTMLResponse)
+async def fork_run(request: Request, run_id: str):
+    src_dir = _run_dir_for_id(run_id)
+    if src_dir is None:
+        return RedirectResponse(url=f"{BASE_PATH}/?error=Invalid%20run%20id", status_code=303)
+
+    client_ip = request.client.host if request.client else "unknown"
+
+    # Forking counts as a convert: enforce daily convert quota
+    if not _consume_rate_limit(client_ip, key="convert", limit=CONVERT_DAILY_LIMIT):
+        logger.info("fork.rate_limit_exceeded from=%s ip=%s", run_id, client_ip)
+        return RedirectResponse(url=f"{BASE_PATH}/?error=Rate%20limit%20exceeded", status_code=303)
+
+    try:
+        new_id = _new_run_id()
+        new_dir = RUNS_DIR / new_id
+        new_dir.mkdir(parents=True, exist_ok=False)
+
+        # Copy a selected set of files so the fork is usable: source .tex, original upload, and common artifacts
+        candidates = list(src_dir.glob("original.*")) + [
+            src_dir / "diagram.tex",
+            src_dir / "diagram.pdf",
+            src_dir / "diagram.png",
+            src_dir / "diagram.svg",
+            src_dir / "preview.png",
+            src_dir / "run.log.txt",
+            src_dir / "meta.json",
+        ]
+        for p in candidates:
+            if p.exists() and p.is_file():
+                shutil.copy2(p, new_dir / p.name)
+
+        # Update or create meta for the new run
+        meta = _read_run_meta(new_dir)
+        meta["forked_from"] = run_id
+        meta["created_at"] = time.time()
+        meta["updated_at"] = time.time()
+        _write_run_meta(new_dir, meta)
+
+        logger.info("fork.ok from=%s to=%s ip=%s", run_id, new_id, client_ip)
+        run_log = RunLogger(new_dir, logger)
+        run_log.line(f"fork.from={run_id} by_ip={client_ip}")
+        run_log.line("rate.consumed key=convert")
+    except Exception:
+        logger.exception("fork.error from=%s", run_id)
+        return RedirectResponse(url=f"{BASE_PATH}/d/{run_id}?error=Fork%20failed", status_code=303)
+
+    return RedirectResponse(url=f"{BASE_PATH}/d/{new_id}", status_code=303)
+
+
 @app.get("/d/{run_id}/files/{filename}")
 async def get_run_file(run_id: str, filename: str):
     path = _safe_join_run_file(run_id, filename)

templates/edit.html

@@ -86,6 +86,15 @@
                                 <i class="fa-solid fa-trash-can icon" aria-hidden="true"></i>
                                 <span>Delete Diagram</span>
                             </button>
+                            <button
+                                class="btn"
+                                type="submit"
+                                formaction="{{ base_path }}/d/{{ run_id }}/fork"
+                                title="Create a copy of this run"
+                            >
+                                <i class="fa-solid fa-code-branch icon" aria-hidden="true"></i>
+                                <span>Fork</span>
+                            </button>
                         </div>
                     </section>
                 </form>
@@ -143,13 +152,14 @@
             const currentTex = latexArea ? latexArea.value : ""
             let historyEntries = []
 
-            // Validate edit/compile/delete actions.
+            // Validate edit/compile/delete/fork actions.
             if (editForm && instructionsInput) {
                 editForm.addEventListener("submit", e => {
                     const submitter = e.submitter
                     const action = (submitter && submitter.getAttribute("formaction")) || ""
                     const isAlternateAction = !!action
                     const isDeleteAction = action.endsWith("/delete")
+                    const isForkAction = action.endsWith("/fork")
                     const val = (instructionsInput.value || "").trim()
 
                     if (isDeleteAction) {
@@ -159,6 +169,13 @@
                         return
                     }
 
+                    if (isForkAction) {
+                        if (!confirm("Create a fork (copy) of this run?")) {
+                            e.preventDefault()
+                        }
+                        return
+                    }
+
                     if (!isAlternateAction && !val) {
                         e.preventDefault()
                     }