fix(agent): tell the model that navigating a page is not reading it

browser_navigate returns the page title and a snapshot reference. It
never returns the page text. Asked to open a URL and summarise it, the
agent called browser_navigate, saw exit_code=0, answered "the page
loaded successfully" and stopped -- having read nothing. It looks like
a successful turn, and the tool log agrees, so nothing flags it.

browser_snapshot has the same trap one level down. Its optional
filename argument is documented as "Save snapshot to markdown file
instead of returning it in the response". The model volunteered a
filename and so received a path it had no way to open: 175 characters
of reference where omitting the argument returns 1634 of content.

Adds a note covering both. Navigate is never the last step, follow it
with browser_snapshot or browser_find; call snapshot with no arguments;
and prefer web_fetch when the task is only to read a page, since it
does the whole thing in one call rather than three round trips -- which
matters on local hardware where each round trip is a full generation.

Injected only when browser tools are in that turn's selection, and
suppressed with the other local-context blocks, so it costs nothing on
unrelated requests. Verified present with browser tools in the set and
absent without.

Observed after the change: the agent that previously stopped at
"the page loaded" went on to call browser_snapshot on its own.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/agent_loop.py

@@ -2412,6 +2412,29 @@ def _build_system_prompt(
             'that open draft is the target: use update_document/edit_document on it instead of creating another document.'
         )
 
+    # Browsing is a two-step tool and models routinely stop after step one.
+    # browser_navigate returns the page TITLE and a snapshot reference — never
+    # the page text. Observed: asked to open a URL and summarise it, the agent
+    # called browser_navigate, saw exit_code=0, reported "the page loaded
+    # successfully", and stopped, having read nothing. browser_snapshot has the
+    # same trap one level down: its optional `filename` argument saves the
+    # snapshot to a file INSTEAD of returning it, and models volunteer one.
+    if relevant_tools and not suppress_local_context and any(
+        "browser_" in str(_t) for _t in relevant_tools
+    ):
+        agent_prompt += (
+            "\n\n🌐 READING A WEB PAGE: browser_navigate only OPENS the page — it returns the "
+            "title and a snapshot reference, never the page text. It is never the last step. "
+            "To read the content you must then call browser_snapshot (or browser_find to look "
+            "for specific text). Reporting that a page 'loaded successfully' is not an answer: "
+            "the user asked what is ON the page. "
+            "Call browser_snapshot with NO arguments. Do NOT pass 'filename' — that writes the "
+            "snapshot to a file INSTEAD of returning it, so you get a path you cannot read and "
+            "the page content is lost. "
+            "When you only need to read a page and not interact with it, web_fetch does it in a "
+            "single call and is preferred."
+        )
+
     # Inject relevant skills based on the user's last message. The
     # SkillsManager does a Jaccard token-match over published skills'
     # name + description + when_to_use + procedure, returning the top