feat: round-limit handling — Continue affordance at the cap + configurable cap (#1999)

* feat: round-limit handling — Continue affordance at the cap + configurable cap

When the agent loop runs out of rounds (per-message step cap, default 20)
while still actively using tools, it stopped silently mid-task. Now:

1. The loop emits a `rounds_exhausted` SSE event at the cap, and the UI shows
   a "Continue" pill at the bottom of the chat that resumes the task from where
   it left off. Repeated cap-hits each get a fresh Continue (multiple continues
   in a row).
2. The cap is configurable in Settings → Agent ("Max steps per message"),
   validated on the client, at the save endpoint, and at the read site.

- src/agent_loop.py: track `_exhausted_rounds` (set only when a full
  tool-executing round completes on the last allowed round — i.e. the agent
  wanted to keep going); emit `{"type":"rounds_exhausted","rounds":N}` (logged).
- routes/chat_routes.py: read `agent_max_rounds` (clamped 1..200), pass as
  `max_rounds`; forward the new event through the SSE relay.
- routes/auth_routes.py: validate numeric settings on save (int + clamp;
  agent_max_rounds 1..200, agent_max_tool_calls 0..1000; 400 on non-int).
- src/settings.py: default `agent_max_rounds = 20`.
- static/: Settings input + client-side clamp; the Continue pill (reuses the
  existing .stopped-indicator / .continue-btn classes and theme vars
  --border/--fg/--bg/--accent); appended to the chat container so it survives
  the message re-render at stream finalize. chat.js cache version bumped.

* test: cover rounds_exhausted emission (cap-hit vs normal finish)

Drives the real stream_agent_loop with mocked LLM stream / tool exec / settings:
a tool block every round exhausts the cap and must emit rounds_exhausted; a
plain answer hits the done-break and must not. Guards the for/else logic.

static/index.html

@@ -1478,6 +1478,10 @@
                 <label class="settings-label">Tool call limit</label>
                 <input id="set-agentMaxTools" type="text" inputmode="numeric" placeholder="0 = unlimited" class="settings-select" style="width:120px;">
               </div>
+              <div class="settings-row">
+                <label class="settings-label">Max steps per message</label>
+                <input id="set-agentMaxRounds" type="text" inputmode="numeric" placeholder="20" class="settings-select" style="width:120px;">
+              </div>
               <div id="set-agentMsg" style="font-size:11px;color:color-mix(in srgb, var(--fg) 45%, transparent);"></div>
             </div>
           </div>
@@ -2092,13 +2096,6 @@
                   <button class="admin-btn-add" id="adm-epAddBtn" style="width:55px;text-align:center;">Add</button>
                 </div>
                 <div id="adm-epApiMsg" class="adm-ep-inline-msg"></div>
-                <div class="adm-copilot-connect">
-                  <button class="admin-btn-sm" id="adm-copilotConnectBtn" type="button" title="Sign in to GitHub Copilot via device flow">
-                    <svg width="13" height="13" viewBox="0 0 24 24" fill="currentColor" style="vertical-align:-2px;margin-right:5px;opacity:0.8"><path d="M12 .5C5.7.5.5 5.7.5 12c0 5.1 3.3 9.4 7.9 10.9.6.1.8-.2.8-.5v-1.7c-3.2.7-3.9-1.5-3.9-1.5-.5-1.3-1.3-1.7-1.3-1.7-1.1-.7.1-.7.1-.7 1.2.1 1.8 1.2 1.8 1.2 1 1.8 2.7 1.3 3.4 1 .1-.8.4-1.3.7-1.6-2.6-.3-5.3-1.3-5.3-5.7 0-1.3.4-2.3 1.2-3.1-.1-.3-.5-1.5.1-3.1 0 0 1-.3 3.3 1.2a11.4 11.4 0 0 1 6 0C17.3 4.7 18.3 5 18.3 5c.6 1.6.2 2.8.1 3.1.8.8 1.2 1.8 1.2 3.1 0 4.4-2.7 5.4-5.3 5.7.4.4.8 1.1.8 2.2v3.3c0 .3.2.6.8.5 4.6-1.5 7.9-5.8 7.9-10.9C23.5 5.7 18.3.5 12 .5z"/></svg>
-                    Connect GitHub Copilot
-                  </button>
-                  <div id="adm-copilotStatus" class="adm-ep-inline-msg"></div>
-                </div>
               </div>
             </div>
           </div>
@@ -2271,7 +2268,7 @@
 <script type="module" src="/static/js/chatRenderer.js"></script>
 <script type="module" src="/static/js/codeRunner.js"></script>
 <script type="module" src="/static/js/chatStream.js"></script>
-<script type="module" src="/static/js/chat.js?v=20260603n"></script>
+<script type="module" src="/static/js/chat.js?v=20260604q"></script>
 <script type="module" src="/static/js/cookbook.js"></script>
 <script type="module" src="/static/js/search-chat.js"></script>
 <script type="module" src="/static/js/compare/index.js"></script>