Phase C: streaming/MCP/shape cleanups + disable quicktype combineClasses

Mirrors PR #1357 Phase C (TypeScript SDK API review).

Changes:

* `SessionConfig.streaming` and `ResumeSessionConfig.streaming` now document
  `Defaults to False` (matches TS PR #1357 4.2).
* `ToolBinaryResult.type` tightened from `str` to `Literal["image", "resource"]`
  with `"image"` default (matches TS PR #1357 2.6).
* `scripts/codegen/python.ts` now sets `inferenceFlags: { combineClasses: false }`
  when invoking quicktype. Previously quicktype's default structural-equality
  merging produced fuzzy synthesized names (e.g.
  `PermissionDecisionApproveForIonApproval` for the merge of
  `PermissionDecisionApproveFor{Session,Location}Approval`), which are
  unstable: any future divergence between the schema variants would silently
  change the generated class name. We rely on the schema's named definitions
  and resolve structural unions explicitly via
  `postProcessRefBasedDiscriminatedUnionsForPython`, so the merging is also
  redundant. Removed the `Session→Ion` / `Location→Ion` acronym hack we
  needed when the merging was on.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

python/copilot/generated/rpc.py

@@ -980,9 +980,10 @@ class SessionConfig(TypedDict, total=False):
     # session telemetry is always disabled regardless of this setting.
     # This is independent of the client OpenTelemetry configuration.
     enable_session_telemetry: bool
-    # Enable streaming of assistant message and reasoning chunks
+    # Enable streaming of assistant message and reasoning chunks.
     # When True, assistant.message_delta and assistant.reasoning_delta events
-    # with delta_content are sent as the response is generated
+    # with delta_content are sent as the response is generated.
+    # Defaults to False.
     streaming: bool
     # Include sub-agent streaming events in the event stream. When True, streaming
     # delta events from sub-agents (e.g., assistant.message_delta,
@@ -1071,7 +1072,7 @@ class ResumeSessionConfig(TypedDict, total=False):
     working_directory: str
     # Override the default configuration directory location.
     config_dir: str
-    # Enable streaming of assistant message chunks
+    # Enable streaming of assistant message chunks. Defaults to False.
     streaming: bool
     # Include sub-agent streaming events in the event stream. When True, streaming
     # delta events from sub-agents (e.g., assistant.message_delta,

python/copilot/session.py

@@ -24,7 +24,7 @@ class ToolBinaryResult:
 
     data: str = ""
     mime_type: str = ""
-    type: str = ""
+    type: Literal["image", "resource"] = "image"
     description: str = ""
 
 

python/copilot/tools.py

@@ -359,14 +359,6 @@ function postProcessRefBasedDiscriminatedUnionsForPython(
             [/Id\b/g, "ID"],
             [/Llm/g, "LLM"],
             [/Cli/g, "CLI"],
-            // quicktype merges structurally-identical unions and synthesizes a
-            // single class name using a common substring. For our schema this
-            // surfaces as e.g. `PermissionDecisionApproveForIonApproval` (merge
-            // of `PermissionDecisionApproveFor{Session,Location}Approval` —
-            // common substring is `Ion`). Try that substitution so we find
-            // and delete the merged blob during union post-processing.
-            [/Session/g, "Ion"],
-            [/Location/g, "Ion"],
         ];
         const results = new Set<string>([name]);
         for (const [pattern, replacement] of substitutions) {
@@ -459,47 +451,6 @@ function postProcessRefBasedDiscriminatedUnionsForPython(
     }
 
     code = applyUnionRewritesToPython(code, resolved);
-
-    // Clean up quicktype-merged blobs that get left behind when quicktype merges
-    // multiple structurally-identical types into one with a synthesized fuzzy
-    // name (e.g. ``PermissionDecisionApproveForIonApproval`` for the merge of
-    // ``PermissionDecisionApproveFor{Session,Location}Approval``). These
-    // blobs are unused after we emit the proper per-variant + union shape.
-    const orphanFuzzyMergedNames = ["PermissionDecisionApproveForIonApproval"];
-    for (const orphanName of orphanFuzzyMergedNames) {
-        const lines = code.split("\n");
-        let classStart = -1;
-        for (let i = 0; i < lines.length; i++) {
-            if (lines[i] === `class ${orphanName}:` || lines[i].startsWith(`class ${orphanName}(`)) {
-                classStart = i;
-                break;
-            }
-        }
-        if (classStart < 0) continue;
-        let blockStart = classStart;
-        while (
-            blockStart > 0 &&
-            (lines[blockStart - 1] === "@dataclass" || /^# /.test(lines[blockStart - 1]))
-        ) {
-            blockStart--;
-        }
-        let blockEnd = classStart + 1;
-        while (blockEnd < lines.length) {
-            const ln = lines[blockEnd];
-            if (
-                /^class \w/.test(ln) ||
-                /^def \w/.test(ln) ||
-                ln === "@dataclass" ||
-                /^# (?:Experimental|Deprecated|Internal):/.test(ln)
-            ) {
-                break;
-            }
-            blockEnd++;
-        }
-        lines.splice(blockStart, blockEnd - blockStart);
-        code = lines.join("\n");
-    }
-
     return { code, unions: resolved };
 }
 
@@ -2789,6 +2740,14 @@ async function generateRpc(schemaPath?: string, sessionEventsSchema?: JSONSchema
         inputData,
         lang: "python",
         rendererOptions: { "python-version": "3.7" },
+        // Disable quicktype's structural-equality merging of class types.
+        // It produces fuzzy synthesized names (e.g. ``PermissionDecisionApproveForIonApproval``
+        // as the merge of ``PermissionDecisionApproveFor{Session,Location}Approval``) which
+        // are unstable: any future divergence between the variants would silently change
+        // the generated class name. We rely on the schema's named definitions and resolve
+        // structural unions via :func:`postProcessRefBasedDiscriminatedUnionsForPython`,
+        // so the merging is also redundant.
+        inferenceFlags: { combineClasses: false },
     });
 
     let typesCode = qtResult.lines.join("\n");