diff --git a/README.md b/README.md
index 43bb2f5..32a5579 100644
--- a/README.md
+++ b/README.md
@@ -227,6 +227,9 @@ Claude Code release and account. The preview flag and contract may change.
 dotline implements the contract described here; it does not promise support
 in every desktop or CLI release.
 
+The channel negotiates MCP `2024-11-05`. Unsupported version requests fall back
+to that implemented revision; handshake-free MCP is not implemented.
+
 `dotline channel` serves JSON-RPC 2.0 over stdio, one object per line. It
 advertises `experimental.claude/channel`, pushes new inbox events and exposes
 one `reply` tool with `message_id` and `text`. Metadata values are strings. It
diff --git a/clients/dotline.sh b/clients/dotline.sh
index 4a99176..64bfe75 100755
--- a/clients/dotline.sh
+++ b/clients/dotline.sh
@@ -119,13 +119,14 @@ json_string() {
 # A tokenizer for the API's flat reply records. Strings are consumed whole,
 # so braces or apparent JSON inside message text cannot change the selection.
 take_string() {
-    local char escape digits
+    local char escape digits codepoint
     parsed=''
     cursor=$((cursor + 1))
     while ((cursor < ${#response})); do
         char=${response:cursor:1}; cursor=$((cursor + 1))
         [[ $char != '"' ]] || return 0
-        [[ $char > $'\x1f' ]] || die 'invalid server JSON'
+        printf -v codepoint '%d' "'$char"
+        ((codepoint < 0 || codepoint >= 32)) || die 'invalid server JSON'
         if [[ $char == '\' ]]; then
             escape=${response:cursor:1}; cursor=$((cursor + 1))
             case "$escape" in
diff --git a/src/dotline/channel.py b/src/dotline/channel.py
index 5658e39..9ccb906 100644
--- a/src/dotline/channel.py
+++ b/src/dotline/channel.py
@@ -112,9 +112,8 @@ def handle(self, message) -> None:
             return
         if method == "initialize":
             self.initialized = True
-            version = params.get("protocolVersion", "2024-11-05")
             self.result(message_id, {
-                "protocolVersion": version if isinstance(version, str) else "2024-11-05",
+                "protocolVersion": "2024-11-05",
                 "capabilities": {"experimental": {"claude/channel": {}}, "tools": {}},
                 "serverInfo": {"name": "dotline", "version": __version__},
                 "instructions": (
diff --git a/tests/test_channel.py b/tests/test_channel.py
index bcc506c..f56a08d 100644
--- a/tests/test_channel.py
+++ b/tests/test_channel.py
@@ -200,6 +200,29 @@ def test_channel_initialize_has_capability_and_policy(mailbox):
     assert "reply tool" in result["instructions"] and "Trust mode: data" in result["instructions"]
 
 
+@pytest.mark.parametrize("params", [
+    {"protocolVersion": "2024-11-05"},
+    {"protocolVersion": "2025-11-25"},
+    {"protocolVersion": "2026-07-28"},
+    {"protocolVersion": "2099-12-31"},
+    {"protocolVersion": "not-a-version"},
+    {"protocolVersion": ""},
+    {},
+    {"protocolVersion": None},
+    {"protocolVersion": 5},
+    {"protocolVersion": True},
+    {"protocolVersion": {}},
+    {"protocolVersion": []},
+])
+def test_channel_initialize_negotiates_implemented_version(mailbox, params):
+    output = QueueOutput()
+    channel = Channel(mailbox[0], stdout=output)
+    channel.handle({"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": params})
+    response = output.lines.get(timeout=2)
+    assert response["jsonrpc"] == "2.0" and response["id"] == 1
+    assert response["result"]["protocolVersion"] == "2024-11-05"
+
+
 def test_channel_lists_only_reply_and_call_appends(mailbox):
     config, store = mailbox
     store.send("Pending before channel start")
diff --git a/tests/test_scripts.py b/tests/test_scripts.py
index a40b4e7..2c05086 100644
--- a/tests/test_scripts.py
+++ b/tests/test_scripts.py
@@ -515,3 +515,24 @@ def test_shell_accepts_complete_send_response(mailbox, invalid_response_server,
     assert result.returncode == 0, result.stderr
     assert result.stdout == expected
     assert len(invalid_response_server.bodies) == 1
+
+
+@pytest.mark.parametrize("invalid_response_server", [
+    (200, b'{"id":7,"ts":"before' + bytes([code]) + b'after"}', False)
+    for code in [1, 9, 10, 13, 31]
+], indirect=True)
+def test_shell_rejects_raw_json_controls(mailbox, invalid_response_server, monkeypatch):
+    result = real_shell_send(mailbox, monkeypatch)
+    assert result.returncode == 1
+    assert result.stdout == ""
+    assert invalid_response_server.bodies[0]["client_id"] in result.stderr
+
+
+@pytest.mark.parametrize("invalid_response_server", [
+    (200, json.dumps({"id": 7, "ts": value}, ensure_ascii=False).encode("utf-8"), False)
+    for value in ["valid-" + chr(127), "café", "snowman ☃", "escaped\nnewline", "escaped-" + chr(31)]
+], indirect=True)
+def test_shell_preserves_valid_json_string_values(mailbox, invalid_response_server, monkeypatch):
+    result = real_shell_send(mailbox, monkeypatch)
+    assert result.returncode == 0, result.stderr
+    assert result.stdout.strip() == "7"