refactor(signal): hygiene cleanups around constants, typing, and config

- Hoist the cell-strip patterns to module level so they match the rest of
  the module's regex style and aren't reparsed on every call.
- Type the markdown transform callback and the mention id walker so the
  inline Callable signature is no longer an untyped Any.
- Add _HTTP_TIMEOUT_SECONDS alongside the other class-level tunables.
- Reject group_message_buffer_size <= 0 in a Pydantic field_validator
  rather than silently disabling the buffer at write time.
- Mark SignalConfig.allow_from as a computed_field so it shows up in
  model_dump() instead of being invisible to serialization.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nanobot/channels/signal.py

@@ -8,12 +8,13 @@ import re
 import shutil
 import unicodedata
 from collections import deque
+from collections.abc import Callable
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Any
 
 import httpx
-from pydantic import Field
+from pydantic import Field, computed_field, field_validator
 
 from nanobot.bus.events import OutboundMessage
 from nanobot.bus.queue import MessageBus
@@ -42,6 +43,18 @@ _SIG_ITALIC_RE = re.compile(r'(?<!\*)\*([^*\n]+)\*(?!\*)|(?<![a-zA-Z0-9_])_([^_\
 _SIG_STRIKE_RE = re.compile(r'~~(.+?)~~|(?<![~\w])~([^~\n]+)~(?![~\w])', re.DOTALL)
 _SIG_TOKEN_RE = re.compile(r'\x00C(\d+)\x00')
 
+# Patterns used to strip inline markdown when rendering table cells as plain
+# text. Defined separately from the styling regexes above because the cell
+# stripper needs a fixed, narrow subset (no single-asterisk italic, no
+# single-tilde strikethrough) and benefits from each pattern's group 1 being
+# the content directly.
+_SIG_CELL_STRIP_PATTERNS: tuple[tuple[re.Pattern, str], ...] = (
+    (re.compile(r'\*\*(.+?)\*\*'), r'\1'),
+    (re.compile(r'__(.+?)__'), r'\1'),
+    (re.compile(r'~~(.+?)~~'), r'\1'),
+    (re.compile(r'`([^`]+)`'), r'\1'),
+)
+
 
 def _utf16_len(s: str) -> int:
     """UTF-16 code-unit length, matching Signal BodyRange semantics."""
@@ -50,10 +63,8 @@ def _utf16_len(s: str) -> int:
 
 def _sig_strip_cell(s: str) -> str:
     """Strip inline markdown from a table cell for plain-text rendering."""
-    s = re.sub(r'\*\*(.+?)\*\*', r'\1', s)
-    s = re.sub(r'__(.+?)__', r'\1', s)
-    s = re.sub(r'~~(.+?)~~', r'\1', s)
-    s = re.sub(r'`([^`]+)`', r'\1', s)
+    for pattern, repl in _SIG_CELL_STRIP_PATTERNS:
+        s = pattern.sub(repl, s)
     return s.strip()
 
 
@@ -132,7 +143,10 @@ def _markdown_to_signal(text: str) -> tuple[str, list[str]]:
     # Phase 2 (run-based): process inline patterns.
     runs: list[_Run] = [_Run(text)]
 
-    def transform(pattern: re.Pattern, make_runs: Any) -> None:
+    def transform(
+        pattern: re.Pattern,
+        make_runs: Callable[[re.Match, frozenset[str]], list[_Run]],
+    ) -> None:
         new_runs: list[_Run] = []
         for run in runs:
             if run.opaque:
@@ -284,6 +298,14 @@ class SignalConfig(Base):
     dm: SignalDMConfig = Field(default_factory=SignalDMConfig)
     group: SignalGroupConfig = Field(default_factory=SignalGroupConfig)
 
+    @field_validator("group_message_buffer_size")
+    @classmethod
+    def _validate_buffer_size(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError("group_message_buffer_size must be > 0")
+        return v
+
+    @computed_field  # type: ignore[prop-decorator]
     @property
     def allow_from(self) -> list[str]:
         """Aggregate allowlist for the base-class is_allowed() check.
@@ -309,6 +331,7 @@ class SignalChannel(BaseChannel):
     display_name = "Signal"
     _TYPING_REFRESH_SECONDS = 10.0
     _MAX_MESSAGE_LEN = 64_000  # signal-cli practical limit (protocol max ~64 KB)
+    _HTTP_TIMEOUT_SECONDS = 60.0
 
     @classmethod
     def default_config(cls) -> dict[str, Any]:
@@ -351,7 +374,9 @@ class SignalChannel(BaseChannel):
                 self.logger.info(f"Connecting to signal-cli daemon at {base_url}...")
 
                 # Create HTTP client
-                self._http = httpx.AsyncClient(timeout=60.0, base_url=base_url)
+                self._http = httpx.AsyncClient(
+                    timeout=self._HTTP_TIMEOUT_SECONDS, base_url=base_url
+                )
 
                 # Test connection
                 try:
@@ -777,9 +802,6 @@ class SignalChannel(BaseChannel):
             message_text: The message content
             timestamp: Message timestamp
         """
-        if self.config.group_message_buffer_size <= 0:
-            return
-
         # Create buffer for this group if it doesn't exist
         if group_id not in self._group_buffers:
             self._group_buffers[group_id] = deque(maxlen=self.config.group_message_buffer_size)
@@ -906,7 +928,7 @@ class SignalChannel(BaseChannel):
         """Extract possible identifier fields from a mention payload."""
         ids: list[str] = []
 
-        def _walk(value: Any, depth: int = 0) -> None:
+        def _walk(value: dict[str, Any] | Any, depth: int = 0) -> None:
             if depth > 2:
                 return
             if not isinstance(value, dict):

tests/channels/test_signal_channel.py

@@ -448,10 +448,13 @@ class TestGroupBuffer:
             ch._add_to_group_buffer("g1", "Alice", "+1111", f"msg{i}", i)
         assert len(ch._group_buffers["g1"]) == 3
 
-    def test_zero_buffer_size_does_not_add(self):
-        ch = _make_channel(group_buffer_size=0)
-        ch._add_to_group_buffer("g1", "Alice", "+1111", "msg", 1000)
-        assert "g1" not in ch._group_buffers
+    def test_zero_buffer_size_rejected_by_validator(self):
+        with pytest.raises(ValueError, match="group_message_buffer_size"):
+            _make_channel(group_buffer_size=0)
+
+    def test_negative_buffer_size_rejected_by_validator(self):
+        with pytest.raises(ValueError, match="group_message_buffer_size"):
+            _make_channel(group_buffer_size=-1)
 
     def test_context_limits_message_length(self):
         ch = _make_channel(group_buffer_size=5)