feat(rag): agent document tools — list/read tools with env-tuned budgets, SSE tool events + "calling tool" UI

Grounded chat turns now run the agent loop (app/rag/agent.py) instead
of a bare chat_stream: while the per-turn budgets last
(BOR_AGENT_LIST_CALLS / BOR_AGENT_READ_CALLS, default 1 each) the model
gets list_documents (the indexed catalog, /api/docs order) and
read_document (full text, never truncated — A7-revised contract); once
both budgets are spent the tools key is dropped from the request and
the model must answer. Rejected calls (unknown tool, unknown/missing
path, document already in context, spent budget) consume no budget.
Budgets 0/0 make exactly one tools=None request — byte-identical to
the pre-phase path (budgets-as-kill-switch). Deflected turns keep the
direct chat_stream (A8 unchanged; the LOW prompt never carries the
<tools> section).

SSE contract gains {"type":"tool","name":...,"argument":
"source/path"|null} frames ahead of the answer deltas (PLAN §4
extension, owner permission 2026-08-26); done.sources, query_log.sources
and the per-turn log line (gains tool_calls=N) report the retrieval
docs + read docs, deduped. The UI shows a "calling tool"
button/label state and one visible .tool-call line per call above the
answer; the lines persist with the chat record and re-render on
reload. chat_stream passes tools through and accumulates streaming
tool_calls deltas into ToolCallPiece (tools=None stays byte-identical).

E2E: deterministic mock tool flow ("use your tools" + <tools> marker:
list -> read first catalog line -> quoted answer) plus the story suite
(marker flow, reload re-render, plain/deflected no-tool regressions).
Docs: .env.example + README (the two tools, the budgets, the SSE tool
frame, the "calling tool" UI state).

probe: turbo tool_calls=supported 2026-08-26 (uv run python -m
scripts.llm_probe --tools — non-streaming + streaming
finish_reason=tool_calls, indexed delta.tool_calls partials)

tests/integration/test_api.py

@@ -192,10 +192,21 @@ def _find_emoji(text: str) -> list[str]:
 )
 def test_ui_chrome_has_no_emoji(client, path: str) -> None:
     """Permanent regression guard (phase 08): the UI chrome — all pages,
-    the JS that renders it, and the stylesheet — is emoji-free."""
+    the JS that renders it, and the stylesheet — is emoji-free.
+
+    Phase 37 revision (owner permission 2026-08-26, PLAN §4): the agent's
+    ``.tool-call`` line carries two CONTENT marks — 🔎 (list) and 📄
+    (read) — the only emoji in the whole frontend, and only as the exact
+    tool-line template strings in app.js. The guard strips precisely
+    those two literals; any other emoji, or those marks anywhere else,
+    still fails."""
     r = client.get(path)
     assert r.status_code == 200
-    assert _find_emoji(r.text) == [], f"emoji found in {path}: {_find_emoji(r.text)!r}"
+    text = r.text
+    if path == "/assets/app.js":
+        text = text.replace('"🔎 Listing documents"', "")
+        text = text.replace('"📄 Reading "', "")
+    assert _find_emoji(text) == [], f"emoji found in {path}: {_find_emoji(text)!r}"
 
 
 def test_chat_requires_message(client) -> None: