refactor(sizing): single mesh packet budget via transport.max_chars (Phase 3) (#5)

Route all mesh message sizing (renderer, digest, reply chunker, NWS
one-packet fit) through the active transport's max_chars instead of
scattered literal 200s. Meshtastic pinned at 200 (byte-identical output);
MeshCore uses its configured ~140. Sets up uniform-to-smaller sizing for
the composite transport. No behavior change on the Meshtastic path.

Co-authored-by: Matt Johnson <mj@k7zvx.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

work/tests/test_uniform_sizing.py

@@ -0,0 +1,244 @@
+"""Tests for Phase 3 uniform mesh-packet sizing.
+
+Verifies that every size-sensitive code path uses the active transport's
+max_chars rather than a hardcoded 200.  Meshtastic default stays 200
+(byte-identical); MeshCore uses 140.
+"""
+
+import sys
+import types
+from unittest.mock import MagicMock
+
+import pytest
+
+# ---------------------------------------------------------------------------
+# Fake meshcore module (must precede production imports that lazy-import it)
+# ---------------------------------------------------------------------------
+
+def _build_fake_meshcore():
+    mod = types.ModuleType("meshcore")
+
+    class EventType:
+        CONTACT_MSG_RECV = "CONTACT_MSG_RECV"
+        CHANNEL_MSG_RECV = "CHANNEL_MSG_RECV"
+        DISCONNECTED = "DISCONNECTED"
+        CONNECTED = "CONNECTED"
+
+    mod.EventType = EventType
+
+    class _FakeMeshCore:
+        self_info = {"public_key": "aabbccdd1122", "name": "FakeNode"}
+        contacts = {}
+
+        async def start_auto_message_fetching(self):
+            pass
+
+        async def stop_auto_message_fetching(self):
+            pass
+
+        async def disconnect(self):
+            pass
+
+        def subscribe(self, event_type, callback):
+            pass
+
+        def get_contact_by_key_prefix(self, prefix):
+            return None
+
+        @classmethod
+        async def create_tcp(cls, host, port,
+                             auto_reconnect=True, max_reconnect_attempts=5):
+            return cls()
+
+        class commands:
+            @staticmethod
+            async def send_chan_msg(chan_idx, text):
+                result = MagicMock()
+                result.is_error.return_value = False
+                return result
+
+            @staticmethod
+            async def send_msg(dst, text):
+                result = MagicMock()
+                result.is_error.return_value = False
+                return result
+
+    mod.MeshCore = _FakeMeshCore
+    return mod
+
+
+sys.modules.setdefault("meshcore", _build_fake_meshcore())
+
+# ---------------------------------------------------------------------------
+# Production imports
+# ---------------------------------------------------------------------------
+
+from meshai.config import ConnectionConfig                        # noqa: E402
+from meshai.connector import MeshtasticTransport                  # noqa: E402
+from meshai.transport.meshcore_transport import MeshCoreTransport  # noqa: E402
+from meshai.transport.factory import build_transport               # noqa: E402
+from meshai.notifications.channels import (                        # noqa: E402
+    MeshBroadcastChannel,
+    MeshDMChannel,
+)
+from meshai.notifications.pipeline import build_pipeline           # noqa: E402
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _mt_config(**overrides):
+    """Return a ConnectionConfig wired for meshtastic (default)."""
+    cfg = ConnectionConfig(transport="meshtastic")
+    for k, v in overrides.items():
+        setattr(cfg, k, v)
+    return cfg
+
+
+def _mc_config(**overrides):
+    """Return a ConnectionConfig wired for meshcore."""
+    cfg = ConnectionConfig(
+        transport="meshcore",
+        meshcore_host="127.0.0.1",
+        meshcore_port=5050,
+        meshcore_channel_index=0,
+    )
+    for k, v in overrides.items():
+        setattr(cfg, k, v)
+    return cfg
+
+
+def _fake_connector(max_chars_val: int):
+    """Minimal fake connector exposing only max_chars."""
+    conn = MagicMock()
+    conn.max_chars = max_chars_val
+    return conn
+
+
+def _minimal_config():
+    """Minimal full Config for build_pipeline calls."""
+    from meshai.config import Config
+    return Config()
+
+
+# ---------------------------------------------------------------------------
+# 1. Transport max_chars property
+# ---------------------------------------------------------------------------
+
+class TestTransportMaxChars:
+    def test_meshtastic_default_is_200(self):
+        cfg = _mt_config()
+        t = MeshtasticTransport(cfg)
+        assert t.max_chars == 200
+
+    def test_meshtastic_respects_config_field(self):
+        cfg = _mt_config(meshtastic_max_chars=160)
+        t = MeshtasticTransport(cfg)
+        assert t.max_chars == 160
+
+    def test_meshcore_default_is_140(self):
+        cfg = _mc_config()
+        t = MeshCoreTransport(cfg)
+        assert t.max_chars == 140
+
+    def test_meshcore_respects_config_field(self):
+        cfg = _mc_config(meshcore_max_chars=120)
+        t = MeshCoreTransport(cfg)
+        assert t.max_chars == 120
+
+    def test_build_transport_meshtastic_max_chars(self):
+        t = build_transport(_mt_config())
+        assert t.max_chars == 200
+
+    def test_build_transport_meshcore_max_chars(self):
+        t = build_transport(_mc_config())
+        assert t.max_chars == 140
+
+
+# ---------------------------------------------------------------------------
+# 2. MeshRenderer char_limit propagation via channels
+# ---------------------------------------------------------------------------
+
+class TestChannelRendererBudget:
+    def test_broadcast_channel_with_meshcore_connector_uses_140(self):
+        conn = _fake_connector(140)
+        ch = MeshBroadcastChannel(connector=conn, channel_index=0)
+        assert ch._renderer._limit == 140
+
+    def test_broadcast_channel_with_meshtastic_connector_uses_200(self):
+        conn = _fake_connector(200)
+        ch = MeshBroadcastChannel(connector=conn, channel_index=0)
+        assert ch._renderer._limit == 200
+
+    def test_dm_channel_with_meshcore_connector_uses_140(self):
+        conn = _fake_connector(140)
+        ch = MeshDMChannel(connector=conn, node_ids=["!aabbccdd"])
+        assert ch._renderer._limit == 140
+
+    def test_dm_channel_with_meshtastic_connector_uses_200(self):
+        conn = _fake_connector(200)
+        ch = MeshDMChannel(connector=conn, node_ids=["!aabbccdd"])
+        assert ch._renderer._limit == 200
+
+
+# ---------------------------------------------------------------------------
+# 3. DigestAccumulator mesh_char_limit propagation via build_pipeline
+# ---------------------------------------------------------------------------
+
+class TestBuildPipelineMeshCharLimit:
+    def test_no_connector_uses_200(self):
+        cfg = _minimal_config()
+        bus = build_pipeline(cfg, llm_backend=None, connector=None)
+        acc = bus._pipeline_components["accumulator"]
+        assert acc._mesh_char_limit == 200
+
+    def test_meshcore_connector_uses_140(self):
+        cfg = _minimal_config()
+        conn = _fake_connector(140)
+        bus = build_pipeline(cfg, llm_backend=None, connector=conn)
+        acc = bus._pipeline_components["accumulator"]
+        assert acc._mesh_char_limit == 140
+
+    def test_meshtastic_connector_uses_200(self):
+        cfg = _minimal_config()
+        conn = _fake_connector(200)
+        bus = build_pipeline(cfg, llm_backend=None, connector=conn)
+        acc = bus._pipeline_components["accumulator"]
+        assert acc._mesh_char_limit == 200
+
+
+# ---------------------------------------------------------------------------
+# 4. Runtime-override durability: survives adapter_config cache invalidation
+# ---------------------------------------------------------------------------
+
+class TestRuntimeOverrideDurability:
+    """Verify set_runtime_override writes are not cleared by invalidate_cache().
+
+    We test at the _resolve/_overrides seam directly because the full
+    adapter_config.nws.single_packet_max_chars read path hits the DB, which
+    is not available in this hermetic test environment.  Testing via _resolve
+    is equivalent: it is the exact call site used by _AdapterSection.__getattr__.
+    """
+
+    def test_override_survives_cache_invalidation(self):
+        from meshai.adapter_config._accessor import (
+            _overrides,
+            _resolve,
+            set_runtime_override,
+            invalidate_cache,
+            _SENTINEL,
+        )
+        key = ("nws", "single_packet_max_chars")
+        try:
+            set_runtime_override("nws", "single_packet_max_chars", 140)
+
+            # Override is visible through the resolution path.
+            assert _resolve("nws", "single_packet_max_chars") == 140
+
+            # Cache invalidation must NOT wipe the override.
+            invalidate_cache()
+            assert _resolve("nws", "single_packet_max_chars") == 140
+        finally:
+            # Clean up so this test cannot pollute subsequent tests.
+            _overrides.pop(key, None)