phase: 95_read_truncation_cap

All gates are green. Final verification is complete — no fixes were needed; the phase is fully implemented and passing.

**Phase 95 final verification report**

- Verified all 3 tasks already implemented (task files in `complete/`): read cap + notice + `ToolResultPiece` (task 01), `tool_result` SSE + live/saved/shared marker (task 02), E2E suite (task 03).
- Code checks passed: `BOR_READ_MAX_CHARS` (default 128 000, validator), pinned `READ_TRUNCATION_NOTICE` + `TRUNCATION_MARKER`, byte-identical at/under-cap read, holder `read_truncations` (no `tool_calls` impact), piece order (after `tool`, before next round), `ChatToolResultEvent`, `ToolCall` back-compat fields, `app.js` live/restore handlers, `shared.js`, `.truncated-note` CSS, `.env.example` entry, mock-LLM echo script.
- **Tests:** `uv run pytest` → 1966 passed; `uv run pytest --cov=app --cov-report=term-missing` → all green, TOTAL **99%** (>90% gate).
- **E2E:** `uv run pytest tests/e2e/test_read_truncation_cap.py -v --no-cov` → **3 passed** (frame order + live marker + LLM notice via echo; save→shared fidelity; short-read control).
- **Regression (isolated):** `test_agent_document_tools` 4 ✓, `test_chat_history` 5 ✓, `test_share_chat` 4 ✓, `test_big_read_progress` 4 ✓, `test_stop_generation` 3 ✓.
- **Lint/types:** `uv run ruff check .` → All checks passed; `uv run pyright` → 0 errors, 0 warnings.

**Completion criteria:** ① over-cap read → first-cap-chars + marker + pinned notice — ✓ (unit-pinned: at-cap/cap+1/notice tests); ② user marker live/saved/shared — ✓ (E2E + frontend tests); ③ at/under cap byte-identical, no frame — ✓ (unit + control E2E); ④ top-2 `<documents>` retrieval untouched — ✓ (`app/rag/retriever.py` unmodified vs HEAD); ⑤ suite green, >90% coverage, ruff+pyright clean — ✓; ⑥ no completed-phase behavior change — ✓ (all gates green; commit left to harness per pass rules).

- No defects found; no changes made this pass. Next pending phase: none in `todo/` (96 is the next free number).

tests/unit/test_prompts.py

@@ -229,6 +229,24 @@ def test_tools_section_phase72_contract_clauses() -> None:
     assert "not a directory or file path" not in TOOLS_SECTION
 
 
+def test_tools_section_phase95_read_truncation_clause() -> None:
+    """Phase 95 (task 01): the ``read`` teaching gains exactly one line —
+    very large documents are capped, a cut read returns the first part
+    plus the TRUNCATED notice (the document did not end where it
+    stopped), and ``grep`` is the follow-up (it searches the whole
+    document). The ``ls``/``grep`` teaching is untouched (phase 94 owns
+    ``ls``) — the clause is pinned byte-for-byte in the constant."""
+    assert (
+        "Very large documents are capped: a cut read returns the first "
+        "part plus a TRUNCATED notice — the document did not end where "
+        "it stopped; use `grep` (pattern) to find the rest, it searches "
+        "the whole document."
+    ) in TOOLS_SECTION
+    # It rides the HIGH prompt and never the LOW (deflected) prompt.
+    doc = _doc("kubernetes.md", "Talos Linux on three nodes.", "Kubernetes")
+    assert "Very large documents are capped" in build_high_prompt([doc])
+
+
 def test_tools_section_phase72_clauses_in_high_prompt_not_low() -> None:
     """Phase 72/94: the contract clauses ride the HIGH prompt with the
     rest of the section and never leak into the LOW/deflection prompt