feat(rag): unbounded agent tool calls behind a round cap (owner revision)

Phase 45 (owner permission 2026-08-27, TODO.md L8: "allow the LLM
to make as many tool calls as it wants"): the phase-37 per-turn tool
budgets (BOR_AGENT_LIST_CALLS / BOR_AGENT_READ_CALLS, default 1 each)
and their exhaustion refusals are removed — a grounded turn now offers
list_documents / read_document for the whole turn (re-lists included),
bounded only by the round cap:

- app/config.py: agent_max_rounds (BOR_AGENT_MAX_ROUNDS, default 10,
  negative rejected) replaces agent_list_calls / agent_read_calls;
  .env.example + README document the single knob; app/rag/prompts.py
  docstrings follow.
- app/rag/agent.py: the loop runs tools until the model answers or
  rounds >= max_rounds, at which point it forces one final no-tools
  answer (the cap is the only forced exit); 0 = no tools — exactly one
  tools=None request, byte-identical to the pre-phase-37 path (the
  kill switch). Rejected calls (unknown tool / missing args /
  already-in-context / unknown path) still consume a round, so
  pathological rejected-call streams are bounded by the cap. The
  per-call log line is now tool/args/round=N/M; the per-turn
  tool_calls=N field and the tool SSE event are unchanged.
- tests/e2e/mock_llm.py: MULTI_READ_TRIGGER ("read two documents") —
  the deterministic list -> read #1 -> read #2 -> forced-answer flow
  (byte-stable "I read <sp1> and <sp2>." line), classified by the
  count of tool-role read results; the phase-37 single-read flow stays
  byte-identical (unit-pinned in tests/unit/test_mock_tool_flow.py).
- tests/e2e/test_agent_unlimited_tools.py (new, story suite,
  mock-only): three tool frames/lines in order (one list, two reads —
  the second read is what the old read budget refused) + the
  both-named non-deflected answer; done.sources + chips = retrieval
  doc + both reads, deduped; no budget refusal rendered; the
  single-read marker flow regression (exactly one read, single tool
  pair).
- .agent/PLAN.md: the phase-45 SSE revision note (owner-locked, R2) —
  the only PLAN edit this phase; the phase-37 note's budget clause is
  marked removed.

Unit/integration rewrites (test_agent.py round-cap matrix incl. the
kill switch and rejected-call spam, test_config.py, test_chat_api.py
agent_max_rounds=0 fixtures) landed with the server core so every gate
stays green.

uv run pytest: 756 passed, app/ coverage 99%; ruff + pyright clean;
story E2E 4/4 in isolation (ran twice); regression E2E suites
(agent_document_tools unmodified, chat_rag, smoke) green in isolation.

Also records the 45_agent_unlimited_tools todo/ -> complete/ task-file
moves (00/01/02 pending in the working tree, task 03 moves on success).

app/rag/prompts.py

@@ -26,9 +26,9 @@ prompt is byte-identical to the pre-phase text.
 
 Agent tools (phase 37): the **HIGH** prompt only carries a ``<tools>``
 section after the ``<documents>`` body — the grounded turn may call the
-server-side ``list_documents`` / ``read_document`` tools (budgeted, see
-:mod:`app.rag.agent`). The LOW/deflection prompt never carries it and
-stays byte-identical to the pre-phase text.
+server-side ``list_documents`` / ``read_document`` tools (round-capped,
+see :mod:`app.rag.agent`). The LOW/deflection prompt never carries it
+and stays byte-identical to the pre-phase text.
 """
 from __future__ import annotations
 
@@ -74,8 +74,8 @@ _KB_INTRO = (
 
 #: The ``<tools>`` instructions section — **HIGH prompt only** (phase 37,
 #: task 03): a grounded turn may extend its context through the two
-#: server-side tools (budgets: ``BOR_AGENT_LIST_CALLS`` /
-#: ``BOR_AGENT_READ_CALLS``, see :mod:`app.rag.agent`). Appended after
+#: server-side tools (round cap: ``BOR_AGENT_MAX_ROUNDS``, see
+#: :mod:`app.rag.agent`). Appended after
 #: the mode body (``<documents>``), so the instructions are the last
 #: thing the model reads. The LOW/deflection prompt never carries it —
 #: a deflection has no grounded context to extend — and stays
@@ -184,8 +184,8 @@ texts of the top documents + the ``<tools>`` instructions (phase 37).
 
     Section order: ``<relevance>`` → ``<knowledge_base>`` → ``<tuning>``
     → ``<documents>`` → ``<tools>``; empty steering/overview omit their
-    section. ``<tools>`` is always present in the HIGH prompt (the
-    budgets — not the prompt — decide whether the tools are actually
+    section. ``<tools>`` is always present in the HIGH prompt (the round
+    cap — not the prompt — decides whether the tools are actually
     offered to the model, see :mod:`app.rag.agent`).
     """
     blocks = [