One chat shell: every content block renders everywhere, plus chat ergonomics (#12598)

.github/checks-manifest.yaml

@@ -264,6 +264,16 @@ checks:
     triggers: ["desktop/macos/Desktop/Sources/**/*.swift", "desktop/macos/scripts/check-grdb-insert-idiom.py", ".github/checks-manifest.yaml"]
     lanes: ["local", "ci"]
     reason: "#11204: a mutating didInsert never witnesses PersistableRecord's non-mutating insert, so a direct record.insert(db) drops the rowid silently onto an optional field; two shipped instances went undetected until unrelated work tripped over them"
+  - id: desktop-single-chat-shell-self-test
+    command: ["python3", "desktop/macos/scripts/check-single-chat-shell.py", "--self-test"]
+    triggers: ["desktop/macos/scripts/check-single-chat-shell.py", ".github/checks-manifest.yaml"]
+    lanes: ["local", "ci"]
+    reason: "the tripwire must keep failing on each shape it was written for, and keep passing on prose that merely names one"
+  - id: desktop-single-chat-shell
+    command: ["python3", "desktop/macos/scripts/check-single-chat-shell.py"]
+    triggers: ["desktop/macos/Desktop/Sources/**/*.swift", "desktop/macos/scripts/check-single-chat-shell.py", ".github/checks-manifest.yaml"]
+    lanes: ["local", "ci"]
+    reason: "#12598: the app mounted one of two shells behind a preference, and six content-block kinds rendered as controls on one and as nothing on the other; both grow back one symbol at a time"
   - id: brand-ui-ratchet-tests
     command: ["python3", ".github/scripts/test_check_brand_ui.py"]
     triggers: [".github/scripts/check_brand_ui.py", ".github/scripts/test_check_brand_ui.py", ".github/checks-manifest.yaml"]

.github/failure-classes/FC-presentation-cohort-drops-journaled-content.json

@@ -0,0 +1,19 @@
+{
+  "schema_version": 1,
+  "id": "FC-presentation-cohort-drops-journaled-content",
+  "violated_contract": "A client-side presentation cohort must never decide whether durable, journaled content is drawn. The macOS chat journaled taskCard, goalLink, captureLink, conversationLink, memoryLink and questionCard blocks for every account, but only the shell sampled into the chat-first cohort was handed a ChatFirstRichBlockContext; every other host (legacy shell, task chat panel, floating bar, notch) decoded the same blocks and rendered EmptyView. A task created during onboarding was therefore in the transcript and invisible, and the same transcript looked different per shell, per cohort, and per surface. The defect reads as 'the task was never created', not as a rendering gate, because the journal is correct.",
+  "canonical_prevention": "One renderer, no optional rendering context: every chat surface receives a non-optional rich-block context, and a behavioural test journals one message carrying every block type and asserts the shared renderer yields the interactable view for each. A static tripwire forbids the retired cohort/legacy symbols and any 'context == nil' branch from returning. Capability gates may disable an action on a card; they may not decide whether the card exists.",
+  "canonical_prevention_artifact": [
+    "desktop/macos/Desktop/Sources/MainWindow/ChatFirst/Blocks/ChatFirstRichBlockGroupView.swift",
+    "desktop/macos/Desktop/Tests/OneChatShellRichBlockTests.swift",
+    "desktop/macos/scripts/check-single-chat-shell.py",
+    "app/test/widgets/chat_content_blocks_test.dart"
+  ],
+  "scope_hints": [
+    "desktop/macos/Desktop/Sources/MainWindow/Components/ChatBubble.swift",
+    "desktop/macos/Desktop/Sources/MainWindow/ChatFirst/**",
+    "app/lib/pages/chat/widgets/**"
+  ],
+  "status": "open",
+  "evidence_prs": []
+}

.github/scripts/check_chat_selection_boundary.py

@@ -9,8 +9,14 @@
 
 SwiftUI has no type-level API that prevents an ancestor or message renderer
 from installing SelectionOverlay. This deliberately narrow source tripwire
-therefore protects the three authoritative live-transcript files. Behavioral
-resize coverage remains in ChatTimelineContinuityTests.
+therefore protects the authoritative live-transcript files. Behavioral resize
+coverage remains in ChatTimelineContinuityTests.
+
+The bar is on `SelectionOverlay`, not on selecting. The transcript now hosts
+selection through `ChatSelectableProse` — one `NSTextView` per prose block,
+which *is* its own selection and installs no per-`Text` overlay for a parent
+rebuild to thrash. That file is protected here too, so the AppKit path can
+never quietly acquire the SwiftUI one.
 """
 
 from __future__ import annotations
@@ -25,13 +31,15 @@
     "desktop/macos/Desktop/Sources/MainWindow/Components/ChatBubble.swift",
     "desktop/macos/Desktop/Sources/MainWindow/Components/ChatMessagesView.swift",
     "desktop/macos/Desktop/Sources/MainWindow/Components/OmiMarkdown.swift",
+    "desktop/macos/Desktop/Sources/MainWindow/Components/ChatSelectableProse.swift",
 )
 MARKDOWN_FILE = LIVE_TRANSCRIPT_FILES[2]
+SELECTION_FILE = LIVE_TRANSCRIPT_FILES[3]
 
 FORBIDDEN_PATTERNS = {
     ".textSelection(.enabled)": (
-        "live chat must not install SwiftUI SelectionOverlay; use the existing copy actions "
-        "or a separate non-live reading surface"
+        "live chat must not install SwiftUI SelectionOverlay; selection belongs to "
+        "ChatSelectableProse, whose NSTextView owns it without one"
     ),
     "textSelectionEnabled": (
         "OmiMarkdown must not expose a native-selection escape hatch"
@@ -59,6 +67,15 @@ def check_sources(sources: Mapping[str, str]) -> list[str]:
             f"{MARKDOWN_FILE}: OmiMarkdown must explicitly disable inherited native text selection"
         )
 
+    # The sanctioned remedy has to stay AppKit. An NSTextView owning its own
+    # selection is the whole reason selection is allowed back into the
+    # transcript; a SwiftUI Text here would reopen the failure class.
+    selection_source = sources.get(SELECTION_FILE)
+    if selection_source is not None and "NSTextView" not in selection_source:
+        failures.append(
+            f"{SELECTION_FILE}: transcript selection must be hosted by an NSTextView"
+        )
+
     return failures
 
 

.github/scripts/test_check_chat_selection_boundary.py

@@ -28,6 +28,11 @@ def clean_sources() -> dict[str, str]:
         CHECKER.MARKDOWN_FILE: (
             "struct OmiMarkdown { var body: some View { Text(text).textSelection(.disabled) } }\n"
         ),
+        CHECKER.SELECTION_FILE: (
+            "struct ChatSelectableProseText: NSViewRepresentable {\n"
+            "  func makeNSView(context: Context) -> NSTextView { ChatProseTextView() }\n"
+            "}\n"
+        ),
     }
 
 
@@ -61,6 +66,19 @@ def test_requires_explicit_disabled_boundary(self) -> None:
 
         self.assertTrue(any("explicitly disable" in failure for failure in failures))
 
+    def test_requires_the_selection_surface_to_stay_appkit(self) -> None:
+        """The remedy is an NSTextView owning its own selection. A SwiftUI
+        rewrite of this file would put SelectionOverlay back in the transcript
+        under a name the pattern check cannot see."""
+        sources = clean_sources()
+        sources[CHECKER.SELECTION_FILE] = (
+            "struct ChatSelectableProseText: View { var body: some View { Text(text) } }\n"
+        )
+
+        failures = CHECKER.check_sources(sources)
+
+        self.assertTrue(any("NSTextView" in failure for failure in failures))
+
     def test_rejects_missing_protected_source(self) -> None:
         sources = clean_sources()
         missing = CHECKER.LIVE_TRANSCRIPT_FILES[1]