feat: default to v1 boundary with autofallback and harden tool-call handling

Author: Nomadcxx

README.md

@@ -290,7 +290,7 @@ CI runs split suites in `.github/workflows/ci.yml`:
 - `unit` job: `bun run test:ci:unit`
 - `integration` job: `bun run test:ci:integration`
 
-Integration CI defaults to OpenCode-owned loop mode:
+Integration CI pins OpenCode-owned loop mode to deterministic settings:
 
 - `CURSOR_ACP_TOOL_LOOP_MODE=opencode`
 - `CURSOR_ACP_PROVIDER_BOUNDARY=v1`
@@ -327,9 +327,11 @@ Set the log level via environment variable:
 - `CURSOR_ACP_LOG_LEVEL=error` - Errors only
 
 Provider-boundary rollout:
+- Default: `CURSOR_ACP_PROVIDER_BOUNDARY=v1`
+- Default: `CURSOR_ACP_PROVIDER_BOUNDARY_AUTOFALLBACK=true`
 - `CURSOR_ACP_PROVIDER_BOUNDARY=legacy` - Original provider/runtime boundary behavior
-- `CURSOR_ACP_PROVIDER_BOUNDARY=v1` - New shared boundary/interception path (recommended)
-- `CURSOR_ACP_PROVIDER_BOUNDARY_AUTOFALLBACK=true` - Emergency fallback from `v1` to `legacy` for the current request only
+- `CURSOR_ACP_PROVIDER_BOUNDARY=v1` - Shared boundary/interception path
+- `CURSOR_ACP_PROVIDER_BOUNDARY_AUTOFALLBACK=false` - Disable fallback and keep strict `v1` behavior
 - `CURSOR_ACP_TOOL_LOOP_MAX_REPEAT=3` - Max repeated failing tool-call fingerprints before guard termination (or fallback when enabled)
 
 Auto-fallback trigger conditions:

src/plugin.ts

@@ -93,7 +93,7 @@ const PROVIDER_BOUNDARY =
     ? LEGACY_PROVIDER_BOUNDARY
     : createProviderBoundary(PROVIDER_BOUNDARY_MODE, CURSOR_PROVIDER_ID);
 const ENABLE_PROVIDER_BOUNDARY_AUTOFALLBACK =
-  process.env.CURSOR_ACP_PROVIDER_BOUNDARY_AUTOFALLBACK === "true";
+  process.env.CURSOR_ACP_PROVIDER_BOUNDARY_AUTOFALLBACK !== "false";
 const TOOL_LOOP_MAX_REPEAT_RAW = process.env.CURSOR_ACP_TOOL_LOOP_MAX_REPEAT;
 const {
   value: TOOL_LOOP_MAX_REPEAT,
@@ -1360,7 +1360,7 @@ export const CursorPlugin: Plugin = async ({ $, directory, client, serverUrl }:
     log.warn("Invalid CURSOR_ACP_TOOL_LOOP_MODE; defaulting to opencode", { value: TOOL_LOOP_MODE_RAW });
   }
   if (!PROVIDER_BOUNDARY_MODE_VALID) {
-    log.warn("Invalid CURSOR_ACP_PROVIDER_BOUNDARY; defaulting to legacy", {
+    log.warn("Invalid CURSOR_ACP_PROVIDER_BOUNDARY; defaulting to v1", {
       value: PROVIDER_BOUNDARY_MODE_RAW,
     });
   }

src/provider/boundary.ts

@@ -54,11 +54,11 @@ export interface ProviderBoundary {
 export function parseProviderBoundaryMode(
   value: string | undefined,
 ): { mode: ProviderBoundaryMode; valid: boolean } {
-  const normalized = (value ?? "legacy").trim().toLowerCase();
+  const normalized = (value ?? "v1").trim().toLowerCase();
   if (normalized === "legacy" || normalized === "v1") {
     return { mode: normalized, valid: true };
   }
-  return { mode: "legacy", valid: false };
+  return { mode: "v1", valid: false };
 }
 
 export function createProviderBoundary(