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/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();