feat(ai): add partial JSON parsing for streaming tool calls

- Added partial-json package for parsing incomplete JSON during streaming
- Tool call arguments now contain partially parsed JSON during toolcall_delta events
- Enables progressive UI updates (e.g., showing file paths before content is complete)
- Arguments are always valid objects (minimum empty {}), never undefined
- Full validation still occurs at toolcall_end when arguments are complete
- Updated all providers (Anthropic, OpenAI Completions/Responses) to use parseStreamingJson
- Added comprehensive documentation and examples in README
- Added test to verify arguments are always defined during streaming

package-lock.json

@@ -1996,6 +1996,12 @@
 				}
 			}
 		},
+		"node_modules/partial-json": {
+			"version": "0.1.7",
+			"resolved": "https://registry.npmjs.org/partial-json/-/partial-json-0.1.7.tgz",
+			"integrity": "sha512-Njv/59hHaokb/hRUjce3Hdv12wd60MtM9Z5Olmn+nehe0QDAsRtRbJPvJ0Z91TusF0SuZRIvnM+S4l6EIP8leA==",
+			"license": "MIT"
+		},
 		"node_modules/pathe": {
 			"version": "2.0.3",
 			"resolved": "https://registry.npmjs.org/pathe/-/pathe-2.0.3.tgz",
@@ -2816,7 +2822,7 @@
 			"version": "0.5.39",
 			"license": "MIT",
 			"dependencies": {
-				"@mariozechner/pi-tui": "^0.5.38",
+				"@mariozechner/pi-tui": "^0.5.39",
 				"@types/glob": "^8.1.0",
 				"chalk": "^5.5.0",
 				"glob": "^11.0.3",
@@ -3205,6 +3211,7 @@
 				"ajv-formats": "^3.0.1",
 				"chalk": "^5.6.2",
 				"openai": "^5.20.0",
+				"partial-json": "^0.1.7",
 				"zod-to-json-schema": "^3.24.6"
 			},
 			"devDependencies": {
@@ -3238,7 +3245,7 @@
 			"version": "0.5.39",
 			"license": "MIT",
 			"dependencies": {
-				"@mariozechner/pi-agent": "^0.5.38",
+				"@mariozechner/pi-agent": "^0.5.39",
 				"chalk": "^5.5.0"
 			},
 			"bin": {