refactor phase 5: ARG cleanup, dispatch-handler arg names

Rename intentionally-unused parameters to underscore-prefixed names at
production sites (cli._echo's ctx, three runtime.server dispatch
handlers' rt arg, _dispatch_envelope's transport arg, and
_materialize_session's envelope arg). Add per-file ARG001/ARG002
ignores for tests/** and examples/** where the unused args are
protocol-mandated tool/handler signatures.

Phase 3 already tightened pyright to fully strict, so the only
remaining Phase-5-class lint families (B006, E722, RUF012, SLF, ARG)
are now all clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nficano

pyproject.toml

@@ -76,7 +76,10 @@ ignore = [
 ]
 
 [tool.ruff.lint.per-file-ignores]
-"tests/**" = ["B011"]
+# Tools (`async def f(ctx, args)`) and inbound handlers (`async def h(env)`)
+# have protocol-mandated signatures; unused-arg lints are noise here.
+"tests/**" = ["B011", "ARG001", "ARG002"]
+"examples/**" = ["ARG001", "ARG002"]
 
 [tool.ruff.lint.pydocstyle]
 convention = "google"

src/arcp/cli.py

@@ -90,7 +90,7 @@ def serve(transport: str, bind: str, token: tuple[str, ...]) -> None:
         )
     )
 
-    async def _echo(ctx: JobContext, args: dict[str, Any]) -> dict[str, Any]:
+    async def _echo(_ctx: JobContext, args: dict[str, Any]) -> dict[str, Any]:
         return {"echo": args}
 
     rt.register_tool("echo", _echo)

src/arcp/runtime/server.py

@@ -237,7 +237,7 @@ async def _handle_cancel(rt: ARCPRuntime, state: SessionState, env: Envelope) ->
                 await rt._send(state, refused)
 
         async def _handle_human_input_response(
-            rt: ARCPRuntime, state: SessionState, env: Envelope
+            _rt: ARCPRuntime, state: SessionState, env: Envelope
         ) -> None:
             cid = env.correlation_id
             if cid is None:
@@ -247,7 +247,7 @@ async def _handle_human_input_response(
             state.pending.resolve(cid, dict(env.payload))
 
         async def _handle_human_choice_response(
-            rt: ARCPRuntime, state: SessionState, env: Envelope
+            _rt: ARCPRuntime, state: SessionState, env: Envelope
         ) -> None:
             cid = env.correlation_id
             if cid is None:
@@ -297,7 +297,7 @@ async def _handle_permission_grant(
             )
 
         async def _handle_permission_deny(
-            rt: ARCPRuntime, state: SessionState, env: Envelope
+            _rt: ARCPRuntime, state: SessionState, env: Envelope
         ) -> None:
             cid = env.correlation_id
             if cid is None:
@@ -615,7 +615,7 @@ async def _sink(env: Envelope) -> None:
         return result.state
 
     async def _dispatch_envelope(
-        self, transport: Transport, state: SessionState, envelope: Envelope
+        self, _transport: Transport, state: SessionState, envelope: Envelope
     ) -> None:
         # Persist inbound for dedupe & resume.
         was_new = await self.event_log.append(envelope)

src/arcp/runtime/session.py

@@ -271,7 +271,7 @@ def _validate_token(self, auth: AuthBlock) -> str:
 
     def _materialize_session(
         self,
-        envelope: Envelope,
+        _envelope: Envelope,
         payload: SessionOpenPayload,
         capabilities: Capabilities,
         principal: str,