server + ui: fix stream routes for model names containing a slash (#26137)

* server + ui: refactor resumable stream routes to query string conv_id

The conversation id can embed a model name containing slashes
(ggml-org/...) in router mode, which the decoded path splits before the
:conv_id param is captured, so stop and resume never matched the
session. Move the id to the conv_id query string on the public routes
and on the internal router -> child hop, where slashes survive
encoding. Handlers are unchanged since query and path params land in
the same map. Add a regression test with a slashed model name.

* server: move stream route docs to server-stream.h

Address review: ngxson wants the main server.cpp registration code kept
clean and simple, with route-level explanations living in the header.
Move the query string rationale and the lookup ownership note next to
the handler declarations in server-stream.h, and shorten the wiring
comment to a pointer.

* server: cancel a pending request when its stream is stopped during model load

The conversation was registered in the conv map only after the blocking
autoload wait, so a stop issued while the model loaded found nothing to
cancel and the request went on to generate an orphan once the load
ended. Register the conversation before the wait and give the entry a
ticket: a stop erases the entry, and the parked request checks its
ticket after the wait and aborts with 400 instead of starting. A newer
request on the same conversation replaces the entry, so only the
stopped request is cancelled. Add a regression test that stops during
the load window.

* server + ui: resume a stream after a page reload during model load

A pending request died with the client socket when the page was
reloaded while its model was loading, so no session ever existed and
the conversation had nothing to recover. A session request that waited
for a load now detaches from the client socket and reaches the child
regardless, the session buffer receives the generation, and the resume
route answers 503 while the owner is loading so the client retries
instead of dropping its state. The WebUI persists the pending stream at
send time, quietly polls on 503, and attaches once the session exists.
Add a regression test that drops the client during the load window.

* ui: show the model load progress again after a page refresh

The resume wait was invisible, so a conversation refreshed while its
model was loading showed nothing until the first byte. On a 503 from
the resume probe, mark the conversation as loading again so the
assistant row persisted at send time renders the processing info, and
target the model frozen in the persisted stream state for the
progress, since the row has no model yet and the dropdown may not be
restored.

* fix CI

* fix CI bis

tools/server/README-dev.md

@@ -136,13 +136,13 @@ Producer side: `server_res_generator` extends `server_res_spipe`, which keeps al
 
 Lifetime safety: the session holds no back reference to the response, so `spipe` is a plain `unique_ptr` touched only by the http worker. `cancel` raises an atomic the producer polls; the producer finalizes the session from its destructor, which also runs `~server_response_reader::stop()` to cancel the generation at the queue level. A `DELETE` stops work by raising the flag and letting the worker unwind.
 
-Consumer side: `GET /v1/stream/<conv_id>?from=N` opens a `text/event-stream` that replays buffered bytes from offset `N` and blocks for live bytes, so the browser reattaches like a fresh EventSource. An offset below the dropped prefix returns 400.
+Consumer side: `GET /v1/stream?conv_id=<id>&from=N` opens a `text/event-stream` that replays buffered bytes from offset `N` and blocks for live bytes, so the browser reattaches like a fresh EventSource. An offset below the dropped prefix returns 400.
 
 Routes:
 
-- `GET /v1/stream/:conv_id?from=N`: replay or live reattach.
+- `GET /v1/stream?conv_id=<id>&from=N`: replay or live reattach. The id travels in the query string because it can embed a model name containing slashes.
 - `POST /v1/streams/lookup` with `{"conversation_ids": [...]}`: returns session status only for ids the caller already owns. There is no listing route, so live sessions cannot be enumerated (an earlier `GET /v1/streams` was removed for exactly this reason).
-- `DELETE /v1/stream/:conv_id`: explicit Stop, idempotent (`evict_and_cancel`).
+- `DELETE /v1/stream?conv_id=<id>`: explicit Stop, idempotent (`evict_and_cancel`).
 
 Router mode binds the same paths to proxy handlers. A `conv_id -> child` map (`conv_models`), populated when a POST is routed, resolves the owning child in one lookup with no polling. The lookup groups ids per child; GET and DELETE proxy straight to the owner. This loopback REST hop is expected to move to a websocket IPC later, swapping only the transport.
 
@@ -166,8 +166,8 @@ graph TD
         GC[GC thread] -- drop after TTL --> Sess
     end
     Sess -- read_from offset --> Cons[stream_pipe_consumer]
-    Cons -- "GET /v1/stream/:id?from=N" --> Client
-    DEL[DELETE /v1/stream/:id] -- evict_and_cancel --> Sess
+    Cons -- "GET /v1/stream?conv_id=id&from=N" --> Client
+    DEL[DELETE /v1/stream?conv_id=id] -- evict_and_cancel --> Sess
 ```
 
 The diagram shows the buffer touch points. The live wire (chunks streamed to the original client during a normal generation) is the producer's default output, described under "Producer side" above.

tools/server/server-models.cpp

@@ -1172,7 +1172,7 @@ bool server_models::ensure_model_ready(const std::string & name) {
     return true;
 }
 
-server_http_res_ptr server_models::proxy_request(const server_http_req & req, const std::string & method, const std::string & name, bool update_last_used) {
+server_http_res_ptr server_models::proxy_request(const server_http_req & req, const std::string & method, const std::string & name, bool update_last_used, bool detached) {
     auto meta = get_meta(name);
     if (!meta.has_value()) {
         throw std::runtime_error("model name=" + name + " is not found");
@@ -1198,7 +1198,10 @@ server_http_res_ptr server_models::proxy_request(const server_http_req & req, co
             req.headers,
             req.body,
             req.files,
-            req.should_stop,
+            // a detached request belongs to a replay session that outlives the client socket:
+            // it reaches the child even when the downstream died during the load wait, the
+            // session buffer is the recipient and DELETE remains the stop
+            detached ? std::function<bool()>([]() { return false; }) : req.should_stop,
             base_params.timeout_read,
             base_params.timeout_write
             );
@@ -1469,13 +1472,9 @@ static bool router_validate_model(std::string & name, server_models & models, bo
     }
     // resolve alias to canonical model name
     name = meta->name;
-    if (models_autoload) {
-        models.ensure_model_ready(name);
-    } else {
-        if (!meta->is_running()) {
-            res_err(res, format_error_response("model is not loaded", ERROR_TYPE_INVALID_REQUEST));
-            return false;
-        }
+    if (!models_autoload && !meta->is_running()) {
+        res_err(res, format_error_response("model is not loaded", ERROR_TYPE_INVALID_REQUEST));
+        return false;
     }
     return true;
 }
@@ -1568,6 +1567,9 @@ void server_models_routes::init_routes() {
         if (!router_validate_model(name, models, autoload, error_res)) {
             return error_res;
         }
+        if (autoload) {
+            models.ensure_model_ready(name);
+        }
         return models.proxy_request(req, method, name, false);
     };
 
@@ -1581,12 +1583,23 @@ void server_models_routes::init_routes() {
             return error_res;
         }
         // remember which child serves this conversation so the stream routes can route straight
-        // to it without polling, keyed on the exact conv id from the header
+        // to it without polling, keyed on the exact conv id from the header. registered before
+        // the load wait so a stop issued while the model loads can erase the entry and cancel
+        // this request instead of leaving an orphan generation
         std::string conv_id = server_stream_conv_id_from_headers(req.headers);
-        if (!conv_id.empty()) {
-            models.conv_models.remember(conv_id, name);
+        uint64_t ticket = models.conv_models.remember(conv_id, name);
+        bool waited = autoload && models.ensure_model_ready(name);
+        if (ticket != 0 && !models.conv_models.alive(conv_id, ticket)) {
+            SRV_INF("request for conv_id=%s cancelled while model name=%s was loading\n",
+                    conv_id.c_str(), name.c_str());
+            res_err(error_res, format_error_response(
+                    "request cancelled by a stop while the model was loading", ERROR_TYPE_INVALID_REQUEST));
+            return error_res;
         }
-        return models.proxy_request(req, method, name, true); // update last usage for POST request only
+        // a session request that waited for a load detaches from the client socket: the
+        // client may have dropped during the wait (page reload) and the session buffer must
+        // still receive the generation for a later resume
+        return models.proxy_request(req, method, name, true, waited && ticket != 0); // update last usage for POST request only
     };
 
     this->post_router_models_load = [this](const server_http_req & req) {
@@ -1779,7 +1792,7 @@ void server_models_routes::init_routes() {
     };
 
     this->router_stream_get = [this](const server_http_req & req) {
-        // GET /v1/stream/<conv_id>?from=N. resolve the owning child from the conv_id -> model
+        // GET /v1/stream?conv_id=<id>&from=N. resolve the owning child from the conv_id -> model
         // map, 404 when nothing maps
         auto res = std::make_unique<server_http_res>();
         std::string conv_id = req.get_param("conv_id");
@@ -1789,13 +1802,24 @@ void server_models_routes::init_routes() {
         }
         std::optional<server_model_meta> owner = resolve_child_for_conv(models, conv_id);
         if (!owner.has_value()) {
-            res_err(res, format_error_response("Stream not found or expired", ERROR_TYPE_NOT_FOUND));
+            // a registered conv whose model is still loading earns a retry: the session appears
+            // once the load ends and the pending request reaches the child
+            auto tracked = models.conv_models.lookup(conv_id);
+            auto meta = tracked.has_value() ? models.get_meta(*tracked) : std::nullopt;
+            bool transient = meta.has_value() && (meta->status == SERVER_MODEL_STATUS_LOADING ||
+                                                  meta->status == SERVER_MODEL_STATUS_DOWNLOADING ||
+                                                  meta->status == SERVER_MODEL_STATUS_DOWNLOADED);
+            if (transient) {
+                res_err(res, format_error_response("Stream owner model is loading, retry later", ERROR_TYPE_UNAVAILABLE));
+            } else {
+                res_err(res, format_error_response("Stream not found or expired", ERROR_TYPE_NOT_FOUND));
+            }
             return res;
         }
         std::string from = req.get_param("from");
-        std::string child_path = "/v1/stream/" + encode_qs(conv_id);
+        std::string child_path = "/v1/stream?conv_id=" + encode_qs(conv_id);
         if (!from.empty()) {
-            child_path += "?from=" + from;
+            child_path += "&from=" + from;
         }
         SRV_TRC("proxying stream resume to model %s on port %d, path=%s\n",
                 owner->name.c_str(), owner->port, child_path.c_str());
@@ -1875,7 +1899,7 @@ void server_models_routes::init_routes() {
     };
 
     this->router_stream_delete = [this](const server_http_req & req) {
-        // DELETE /v1/stream/<conv_id>. resolve the owning child via the map and forward only to
+        // DELETE /v1/stream?conv_id=<id>. resolve the owning child via the map and forward only to
         // it, evict_and_cancel is idempotent on the child
         auto res = std::make_unique<server_http_res>();
         std::string conv_id = req.get_param("conv_id");
@@ -1883,7 +1907,7 @@ void server_models_routes::init_routes() {
             res_err(res, format_error_response("Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST));
             return res;
         }
-        std::string child_path = "/v1/stream/" + encode_qs(conv_id);
+        std::string child_path = "/v1/stream?conv_id=" + encode_qs(conv_id);
         auto owner = resolve_child_for_conv(models, conv_id);
         if (owner.has_value()) {
             httplib::Client cli(CHILD_ADDR, owner->port);
@@ -1892,6 +1916,11 @@ void server_models_routes::init_routes() {
             cli.set_write_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
             auto resp = cli.Delete(child_path.c_str());
             (void) resp; // the child logs its own miss when the session is unknown there
+        } else if (auto tracked = models.conv_models.lookup(conv_id); tracked.has_value()) {
+            // the entry exists but its model is still loading: the forget below erases it,
+            // which cancels the request parked in proxy_post before the generation starts
+            SRV_INF("router stop for conv_id=%s while model name=%s is loading, cancelling the pending request\n",
+                    conv_id.c_str(), tracked->c_str());
         } else {
             SRV_WRN("router stop for unknown conv_id=%s, no owning child in the conv map\n",
                     conv_id.c_str());

tools/server/server-models.h

@@ -134,12 +134,24 @@ private:
     // proxy_request forwards a POST carrying an X-Conversation-Id. best effort: a stale entry just
     // makes the child answer not found and the client recovers. owns its lock, one mutex per struct
     struct conv_model_tracker {
-        void remember(const std::string & conv_id, const std::string & model) {
+        // returns the ticket of this registration, 0 when nothing was registered. erasing or
+        // replacing the entry invalidates the ticket, which is how a stop cancels a request
+        // parked in the model load wait
+        uint64_t remember(const std::string & conv_id, const std::string & model) {
             if (conv_id.empty() || model.empty()) {
-                return;
+                return 0;
             }
             std::lock_guard<std::mutex> lock(mu);
-            map[conv_id] = model;
+            uint64_t ticket = next_ticket++;
+            map[conv_id] = { model, ticket };
+            return ticket;
+        }
+
+        // false means a stop erased the entry or a newer request replaced it
+        bool alive(const std::string & conv_id, uint64_t ticket) {
+            std::lock_guard<std::mutex> lock(mu);
+            auto it = map.find(conv_id);
+            return it != map.end() && it->second.ticket == ticket;
         }
 
         std::optional<std::string> lookup(const std::string & conv_id) {
@@ -151,7 +163,7 @@ private:
             if (it == map.end()) {
                 return std::nullopt;
             }
-            return it->second;
+            return it->second.model;
         }
 
         void forget(const std::string & conv_id) {
@@ -163,8 +175,13 @@ private:
         }
 
       private:
-        std::mutex                                   mu;
-        std::unordered_map<std::string, std::string> map;
+        struct entry_t {
+            std::string model;
+            uint64_t    ticket;
+        };
+        std::mutex                               mu;
+        uint64_t                                 next_ticket = 1;
+        std::unordered_map<std::string, entry_t> map;
     };
 
     common_preset_context ctx_preset;
@@ -249,7 +266,7 @@ public:
     bool ensure_model_ready(const std::string & name);
 
     // proxy an HTTP request to the model instance
-    server_http_res_ptr proxy_request(const server_http_req & req, const std::string & method, const std::string & name, bool update_last_used);
+    server_http_res_ptr proxy_request(const server_http_req & req, const std::string & method, const std::string & name, bool update_last_used, bool detached = false);
 
     // handle message sent from server_child::notify_to_router()
     // raw input must starts with CMD_CHILD_TO_ROUTER_STATE, followed by a JSON string

tools/server/server-stream.cpp

@@ -453,7 +453,7 @@ static server_http_res_ptr make_error_response(int status, const std::string & m
 
 server_http_context::handler_t server_stream_make_get_handler() {
     return [](const server_http_req & req) -> server_http_res_ptr {
-        // GET /v1/stream/<conv_id>?from=N replays buffered SSE bytes then blocks for live
+        // GET /v1/stream?conv_id=<id>&from=N replays buffered SSE bytes then blocks for live
         // bytes until the session finalizes, streamed as text/event-stream for EventSource
         std::string conv_id = req.get_param("conv_id");
         if (conv_id.empty()) {
@@ -560,13 +560,13 @@ server_http_context::handler_t server_stream_make_lookup_handler() {
 
 server_http_context::handler_t server_stream_make_delete_handler() {
     return [](const server_http_req & req) -> server_http_res_ptr {
-        // DELETE /v1/stream/<conv_id> is the explicit user Stop, cancels the producer and evicts
+        // DELETE /v1/stream?conv_id=<id> is the explicit user Stop, cancels the producer and evicts
         // the buffer. idempotent, returns 204 even if the session was already gone
         std::string conv_id = req.get_param("conv_id");
         if (conv_id.empty()) {
             return make_error_response(400, "Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST);
         }
-        SRV_TRC("DELETE /v1/stream/%s -> evict_and_cancel\n", conv_id.c_str());
+        SRV_TRC("DELETE /v1/stream conv_id=%s -> evict_and_cancel\n", conv_id.c_str());
         g_stream_sessions.evict_and_cancel(conv_id);
         auto res = std::make_unique<server_http_res>();
         res->status = 204;
@@ -621,7 +621,7 @@ bool server_res_spipe::conn_alive() {
 
 bool server_res_spipe::should_stop() {
     if (spipe) {
-        // note: if DELETE /v1/stream/<conv_id> is called, is_cancelled() will be true
+        // note: if DELETE /v1/stream is called for this conv, is_cancelled() will be true
         return spipe->is_cancelled();
     } else {
         return !conn_alive();

tools/server/server-stream.h

@@ -45,7 +45,13 @@ void server_stream_session_manager_start();
 void server_stream_session_manager_stop();
 
 // route handler factories wired under /v1/stream/* by server.cpp
+// child-side handlers for the resumable stream routes. the conv id travels in the conv_id
+// query string because it can embed a model name containing slashes (org/repo), which the
+// decoded path would split before the param is captured
 server_http_context::handler_t server_stream_make_get_handler();
+// POST /v1/streams/lookup with body {"conversation_ids": [...]}: only answers for ids the
+// caller already owns (the WebUI passes the convs visible in its sidebar), the server never
+// lists ids it has not been asked about, so a random caller cannot enumerate live sessions
 server_http_context::handler_t server_stream_make_lookup_handler();
 server_http_context::handler_t server_stream_make_delete_handler();
 

tools/server/server.cpp

@@ -272,10 +272,8 @@ int llama_server(common_params & params, int argc, char ** argv) {
     ctx_http.get ("/slots",                    ex_wrapper(routes.get_slots));
     ctx_http.post("/slots/:id_slot",           ex_wrapper(routes.post_slots));
 
-    // resumable streaming, the conversation_id is the session identity end to end. router and
-    // child wire different handlers under the same paths: a child binds the local session
-    // factories, the router binds proxies that resolve the owning child through the
-    // conv_id -> model map
+    // resumable streaming: a child binds the local session factories, the router binds
+    // proxies that resolve the owning child, see server-stream.h
     server_http_context::handler_t stream_get_h;
     server_http_context::handler_t streams_lookup_h;
     server_http_context::handler_t stream_delete_h;
@@ -288,12 +286,9 @@ int llama_server(common_params & params, int argc, char ** argv) {
         streams_lookup_h = server_stream_make_lookup_handler();
         stream_delete_h  = server_stream_make_delete_handler();
     }
-    ctx_http.get ("/v1/stream/:conv_id",       ex_wrapper(stream_get_h));
-    // POST /v1/streams/lookup with body {"conversation_ids": [...]}. you can only ask for ids
-    // you already own (the WebUI passes the convs visible in its sidebar). the server never
-    // lists ids it has not been asked about, so a random caller cannot enumerate live sessions
+    ctx_http.get ("/v1/stream",                ex_wrapper(stream_get_h));
     ctx_http.post("/v1/streams/lookup",        ex_wrapper(streams_lookup_h));
-    ctx_http.del ("/v1/stream/:conv_id",       ex_wrapper(stream_delete_h));
+    ctx_http.del ("/v1/stream",                ex_wrapper(stream_delete_h));
 
     // Google Cloud Platform (Vertex AI) compat
     ctx_http.register_gcp_compat();

tools/server/tests/unit/test_stream.py

@@ -0,0 +1,153 @@
+import json
+import socket
+import threading
+import time
+from urllib.parse import quote
+import pytest
+from utils import *
+
+server: ServerProcess
+
+# a model name with slashes exercises the query string routing of the stream routes: the id
+# cannot travel as a path param because the decoded slash would split it before capture
+MODEL = "ggml-org/tinygemma3-GGUF:Q8_0"
+STREAM_ID = f"conv-stream-test::{MODEL}"
+QS = "conv_id=" + quote(STREAM_ID, safe="")
+
+
+@pytest.fixture(autouse=True)
+def create_server():
+    global server
+    server = ServerPreset.router()
+
+
+def test_stream_resume_and_stop_with_slashed_model_name():
+    global server
+    server.start()
+
+    content = ""
+    for data in server.make_stream_request("POST", "/chat/completions", data={
+        "model": MODEL,
+        "stream": True,
+        "max_tokens": 16,
+        "messages": [{"role": "user", "content": "hello"}],
+    }, headers={"X-Conversation-Id": STREAM_ID}):
+        if data["choices"]:
+            content += data["choices"][0]["delta"].get("content") or ""
+    assert len(content) > 0
+
+    # the finished session replays from the beginning through the router
+    res = server.make_request("GET", f"/v1/stream?{QS}&from=0")
+    assert res.status_code == 200
+    assert "data: " in str(res.body)
+
+    # the explicit stop reaches the owning child and evicts the session
+    res = server.make_request("DELETE", f"/v1/stream?{QS}")
+    assert res.status_code == 204
+    res = server.make_request("GET", f"/v1/stream?{QS}&from=0")
+    assert res.status_code == 404
+
+
+def test_stream_stop_during_model_load():
+    global server
+    server.start()
+
+    thread_error: list[ServerError] = []
+    thread_done = threading.Event()
+
+    def fire_post():
+        try:
+            for _ in server.make_stream_request("POST", "/chat/completions", data={
+                "model": MODEL,
+                "stream": True,
+                "max_tokens": 512,
+                "messages": [{"role": "user", "content": "Count from 1 to 1000."}],
+            }, headers={"X-Conversation-Id": STREAM_ID}):
+                pass
+        except ServerError as e:
+            thread_error.append(e)
+        finally:
+            thread_done.set()
+
+    t = threading.Thread(target=fire_post)
+    t.start()
+
+    # catch the autoload window, tiny models load fast so poll aggressively
+    saw_loading = False
+    deadline = time.time() + 5.0
+    while time.time() < deadline and not thread_done.is_set():
+        res = server.make_request("GET", "/models")
+        status = next(m["status"]["value"] for m in res.body["data"] if m["id"] == MODEL)
+        if status == "loading":
+            saw_loading = True
+            break
+        time.sleep(0.002)
+    if not saw_loading:
+        t.join()
+        pytest.skip("load window too short to be observed on this machine")  # ty: ignore[too-many-positional-arguments]
+
+    # a stop during the load cancels the parked request instead of leaving an orphan
+    res = server.make_request("DELETE", f"/v1/stream?{QS}")
+    assert res.status_code == 204
+    assert thread_done.wait(timeout=60)
+    t.join()
+    assert len(thread_error) == 1
+    assert thread_error[0].code == 400
+    assert "cancelled" in json.dumps(thread_error[0].body)
+    res = server.make_request("GET", f"/v1/stream?{QS}&from=0")
+    assert res.status_code == 404
+
+
+def test_stream_resumes_after_reload_during_model_load():
+    global server
+    server.start()
+
+    # raw socket client so the connection can be dropped mid load like a page reload
+    body = json.dumps({
+        "model": MODEL,
+        "stream": True,
+        "max_tokens": 16,
+        "messages": [{"role": "user", "content": "hello"}],
+    })
+    request = (
+        f"POST /v1/chat/completions HTTP/1.1\r\n"
+        f"Host: {server.server_host}:{server.server_port}\r\n"
+        f"Content-Type: application/json\r\n"
+        f"X-Conversation-Id: {STREAM_ID}\r\n"
+        f"Content-Length: {len(body)}\r\n"
+        f"Connection: close\r\n\r\n{body}"
+    )
+    sock = socket.create_connection((server.server_host, server.server_port))
+    sock.sendall(request.encode())
+
+    # drop the client while the model loads, poll aggressively to catch the window
+    saw_loading = False
+    saw_503 = False
+    deadline = time.time() + 5.0
+    while time.time() < deadline:
+        res = server.make_request("GET", "/models")
+        status = next(m["status"]["value"] for m in res.body["data"] if m["id"] == MODEL)
+        if status == "loading":
+            saw_loading = True
+            break
+        if status == "loaded":
+            break
+        time.sleep(0.002)
+    sock.close()
+    if not saw_loading:
+        pytest.skip("load window too short to be observed on this machine")  # ty: ignore[too-many-positional-arguments]
+
+    # while the model loads the resume route answers retry later, then the session appears,
+    # receives the whole generation despite the dead client, and replays from the beginning
+    deadline = time.time() + 60.0
+    replay = None
+    while time.time() < deadline:
+        res = server.make_request("GET", f"/v1/stream?{QS}&from=0")
+        if res.status_code == 503:
+            saw_503 = True
+        elif res.status_code == 200 and "data: " in str(res.body):
+            replay = res
+            break
+        time.sleep(0.1)
+    assert saw_503, "resume during the load did not answer 503"
+    assert replay is not None, "session never became resumable after the client disconnect"

tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageAssistant/ChatMessageAssistant.svelte

@@ -10,7 +10,7 @@
 	} from '$lib/components/app';
 	import { getMessageEditContext } from '$lib/contexts';
 	import { useProcessingState } from '$lib/hooks/use-processing-state.svelte';
-	import { isLoading, isChatStreaming } from '$lib/stores/chat.svelte';
+	import { chatStore, isLoading, isChatStreaming } from '$lib/stores/chat.svelte';
 	import { modelLoadProgressText } from '$lib/utils';
 	import { MessageRole } from '$lib/enums';
 	import { config } from '$lib/stores/settings.svelte';
@@ -82,8 +82,11 @@
 	let hasNoContent = $derived(!message?.content?.trim());
 	let isActivelyProcessing = $derived(isCurrentlyLoading || isStreaming);
 
-	// during a router auto-load the message has no model yet, so target the selected one
-	let loadTargetModel = $derived(message.model ?? modelsStore.selectedModelName);
+	// during a router auto-load the message has no model yet: target the model frozen in the
+	// persisted stream state (survives a reload), then fall back to the dropdown selection
+	let loadTargetModel = $derived(
+		message.model ?? chatStore.getResumeModel(message.convId) ?? modelsStore.selectedModelName
+	);
 	let modelLoadProgress = $derived(
 		isRouter && loadTargetModel ? modelsStore.getLoadProgress(loadTargetModel) : null
 	);

tools/ui/src/lib/constants/api-endpoints.ts

@@ -21,7 +21,11 @@ export const API_TOOLS = {
 	EXECUTE: '/tools'
 };
 
-// resumable stream routes, the conv::model identity is appended as a path segment
+// resumable stream routes, the conv::model identity travels as the conv_id query param
+// because model names can contain slashes that a path segment cannot carry
+// resume retry cadence while the owning model is still loading (server answers 503)
+export const STREAM_RESUME_RETRY_MS = 2000;
+
 export const API_STREAM = {
 	BASE: './v1/stream',
 	LOOKUP: './v1/streams/lookup'

tools/ui/src/lib/services/chat.service.ts

@@ -343,6 +343,9 @@ export class ChatService {
 			// model the ::model suffix keeps the per model session distinct
 			if (stream && conversationId) {
 				headers['X-Conversation-Id'] = streamIdentity(conversationId, options.model);
+				// persist the pending stream before the fetch: a reload during the model load or
+				// the prompt processing must still find its way back to the session once it exists
+				ChatService.saveStreamState(conversationId, 0, options.model ?? null);
 			}
 
 			const response = await fetch(API_CHAT.COMPLETIONS, {
@@ -353,6 +356,11 @@ export class ChatService {
 			});
 
 			if (!response.ok) {
+				// a rejected request (including one cancelled by a stop during the model load)
+				// leaves nothing to resume
+				if (conversationId) {
+					ChatService.clearStreamState(conversationId);
+				}
 				const error = await ChatService.parseErrorResponse(response);
 
 				if (onError) {
@@ -512,7 +520,7 @@ export class ChatService {
 		if (!conversationId) return;
 		try {
 			const id = streamIdentity(conversationId, model);
-			await fetch(`${API_STREAM.BASE}/${encodeURIComponent(id)}`, {
+			await fetch(`${API_STREAM.BASE}?conv_id=${encodeURIComponent(id)}`, {
 				method: 'DELETE',
 				headers: getAuthHeaders()
 			});
@@ -605,6 +613,26 @@ export class ChatService {
 	 * existing SSE parser drains it like a fresh stream. The server returns 200 on success, 404 if
 	 * no session exists for the conv_id, and 400 if the offset is below the dropped prefix.
 	 */
+	// probe the resume route status without consuming the stream: the SSE route has no HEAD,
+	// so issue the GET and abort it right after the status line. 0 on network error
+	static async probeResumeStatus(streamId: string): Promise<number> {
+		if (!streamId) return 0;
+		const ac = new AbortController();
+		try {
+			const resp = await fetch(
+				`${API_STREAM.BASE}?conv_id=${encodeURIComponent(streamId)}&from=0`,
+				{
+					headers: getAuthHeaders(),
+					signal: ac.signal
+				}
+			);
+			ac.abort();
+			return resp.status;
+		} catch {
+			return 0;
+		}
+	}
+
 	static async resumeStream(
 		conversationId: string,
 		signal?: AbortSignal,
@@ -614,7 +642,7 @@ export class ChatService {
 		const state = ChatService.getStreamState(conversationId);
 		const from = state?.bytesReceived ?? 0;
 		const id = streamIdentity(conversationId, model);
-		const url = `${API_STREAM.BASE}/${encodeURIComponent(id)}?from=${from}`;
+		const url = `${API_STREAM.BASE}?conv_id=${encodeURIComponent(id)}&from=${from}`;
 		return await fetch(url, { method: 'GET', signal, headers: getAuthHeaders() });
 	}
 

tools/ui/src/lib/stores/chat.svelte.ts

@@ -14,6 +14,7 @@
 import { SvelteMap, SvelteSet } from 'svelte/reactivity';
 import { DatabaseService } from '$lib/services/database.service';
 import { ChatService } from '$lib/services/chat.service';
+import { STREAM_RESUME_RETRY_MS } from '$lib/constants/api-endpoints';
 import { streamIdentity } from '$lib/utils/stream-identity';
 import { getAuthHeaders } from '$lib/utils/api-headers';
 import { CONTENT_TYPE_HEADER } from '$lib/constants';
@@ -78,7 +79,7 @@ class ChatStore {
 	// true while the active conversation streams reasoning content but no visible content yet
 	isReasoning = $state(false);
 	// resumable stream connection state for the active conversation
-	// streaming -> bytes flowing normally, resuming -> waiting on /v1/stream/:id reconnect, lost -> unrecoverable
+	// streaming -> bytes flowing normally, resuming -> waiting on /v1/stream reconnect, lost -> unrecoverable
 	streamConnectionState = $state<StreamConnectionState>(StreamConnectionState.STREAMING);
 	chatLoadingStates = new SvelteMap<string, boolean>();
 	chatReasoningStates = new SvelteMap<string, boolean>();
@@ -94,6 +95,11 @@ class ChatStore {
 	// off when one conv finishes while another is still streaming. mirrors chatLoadingStates
 	// in scope but tracks the attach + tee replay path specifically
 	private attachingConvs = new SvelteSet<string>();
+	// pending resume retry timers while an owning model loads, one per conv
+	private resumeRetryTimers = new SvelteMap<string, ReturnType<typeof setTimeout>>();
+	// convs whose resume waits on a model load: their loading state belongs to the retry loop,
+	// so discoverActiveStream must not treat it as a live send and bail
+	private resumePendingConvs = new SvelteSet<string>();
 	// in-flight discoverActiveStream guard, keyed by conv id
 	private discoveringConvs = new SvelteSet<string>();
 	private abortControllers = new SvelteMap<string, AbortController>();
@@ -263,7 +269,7 @@ class ChatStore {
 		const id = streamId || streamIdentity(convId, selectedModelName());
 		let response: Response;
 		try {
-			response = await fetch(`./v1/stream/${encodeURIComponent(id)}?from=0`, {
+			response = await fetch(`./v1/stream?conv_id=${encodeURIComponent(id)}&from=0`, {
 				headers: getAuthHeaders()
 			});
 		} catch (e) {
@@ -438,13 +444,22 @@ class ChatStore {
 		}
 	}
 
+	/**
+	 * Model frozen at send time for a stream awaiting resume, from the persisted stream state.
+	 * The load progress indicator targets it after a reload, when the message row has no model
+	 * yet and the dropdown selection may not be restored.
+	 */
+	getResumeModel(convId: string): string | null {
+		return ChatService.getStreamState(convId)?.model ?? null;
+	}
+
 	async discoverActiveStream(convId: string): Promise<void> {
 		if (!convId) return;
 		if (this.chatStreamingStates.has(convId)) return;
-		if (this.chatLoadingStates.get(convId)) return;
+		if (this.chatLoadingStates.get(convId) && !this.resumePendingConvs.has(convId)) return;
 		// concurrency guard: another discover may already be running for this conv (typical race
 		// between mount and visibilitychange on tab switch). a second concurrent fetch on the same
-		// /v1/stream/<id> would duplicate every byte into the DB message, this guard bounces it
+		// /v1/stream would duplicate every byte into the DB message, this guard bounces it
 		if (this.discoveringConvs.has(convId)) return;
 		this.discoveringConvs.add(convId);
 
@@ -470,6 +485,38 @@ class ChatStore {
 			if (!localState) {
 				return;
 			}
+			// quiet status probe first: a full attach flips the loading UI on every try, probing
+			// keeps the retry loop invisible while the owning model is still loading (503)
+			const status = await ChatService.probeResumeStatus(streamId);
+			if (status === 503) {
+				// make the wait visible: the empty assistant row persisted at send time renders
+				// the processing info, whose model load percentage flows from the models feed
+				this.resumePendingConvs.add(convId);
+				this.setChatLoading(convId, true);
+				if (!this.resumeRetryTimers.has(convId)) {
+					this.resumeRetryTimers.set(
+						convId,
+						setTimeout(() => {
+							this.resumeRetryTimers.delete(convId);
+							void this.discoverActiveStream(convId);
+						}, STREAM_RESUME_RETRY_MS)
+					);
+				}
+				return;
+			}
+			if (this.resumePendingConvs.delete(convId) && status !== 200) {
+				// the wait is over without a session to attach, drop the visible loading state
+				this.setChatLoading(convId, false);
+			}
+			if (status === 0) {
+				// transient network failure, the next mount or visibility change retries
+				return;
+			}
+			if (status !== 200) {
+				// the session is gone (stopped, TTL expired), nothing to resume anymore
+				ChatService.clearStreamState(convId);
+				return;
+			}
 			await this.attachServerStream(convId, streamId);
 			// if attachServerStream failed (session gone, TTL expired), clear the local state to avoid retrying forever
 			if (!this.chatStreamingStates.has(convId) && !this.chatLoadingStates.get(convId)) {
@@ -1469,8 +1516,16 @@ class ChatStore {
 		// detached drain keeps producing tokens until eos or max_tokens. use the frozen identity
 		// captured when the session started, not the live dropdown
 		const streamStateForStop = this.chatStreamingStates.get(convId);
-		const modelForStop = streamStateForStop?.model;
+		const modelForStop = streamStateForStop?.model ?? ChatService.getStreamState(convId)?.model;
 		void ChatService.cancelServerStream(convId, modelForStop);
+		// an explicit stop leaves nothing to resume and kills a pending resume retry
+		ChatService.clearStreamState(convId);
+		const retryTimer = this.resumeRetryTimers.get(convId);
+		if (retryTimer !== undefined) {
+			clearTimeout(retryTimer);
+			this.resumeRetryTimers.delete(convId);
+		}
+		this.resumePendingConvs.delete(convId);
 		this.abortRequest(convId);
 		this.setChatLoading(convId, false);
 		this.clearChatStreaming(convId);