fix(panel): the terminal mapping half --- classification, domain, publication

Three of the four terminal gaps. The fourth is recorded as owed rather
than faked; see below.

**THE STABLE CLASSIFICATION WAS INCOMPLETE.** Cursor motion still
advanced the mapping revision: `restore_cursor`, `horizontal_tab`,
`move_vertical`, `move_horizontal`, `set_col` and `set_row` all called
`changed()`. Moving the caret denotes nothing new, and a child that
merely repositions its cursor would have cancelled a drag. All six take
the display-only path now.

Worse, **rewriting the same glyph under another style advanced it**,
which is precisely the control SS5b requires to hold. `write_character`
now compares the glyph before writing --- sampled BEFORE
`clear_wide_at`, which blanks a cell that is part of a wide pair and
would otherwise make every rewrite look like a change. That ordering
was found by instrumenting the failing row, not by reading the code.

**THE SNAPSHOT CARRIED DOCUMENT-ONLY STATE FOR TERMINALS.**
`view_top`, `view_left`, wrap, content columns, fold policy and folds
describe a document projection and take no part in a terminal's, where
the child's screen decides the mapping. They live inside the `Document`
arm now; only common geometry --- buffer identity, rows, columns ---
stays outside.

**AND THE REVISION WAS NOT PUBLICATION-CONSISTENT.**
`view_mapping_identity` read the LIVE screen revision while
`projection_ref` returns the last PUBLISHED cells, so buffered output
under synchronized-output would stamp displayed cells with authority
they were never painted under --- a frontend echoing a generation
matching nothing it can see. `ScreenProjection` carries
`mapping_revision` now and the published value is what is read.

**The witnesses were separated across the seam**, which review named
exactly: `screen.rs` proved the counter, the daemon proved enum
selection, and a `view_mapping_identity` returning a constant would
have left both green. A daemon-level row now drives real events through
a panel terminal and asserts the daemon's generation moves on a new
glyph and holds across a style-only rewrite and across cursor motion.

**OWED, NOT DONE: the scroll-anchor row.** The anchor is in the key,
but three attempts failed to drive a scroll from this fixture ---
`scroll_lines` wants a viewport the projection registers on its own
schedule, and `scroll_view` with an explicit size reports no movement
after forty line feeds. Recorded in the ledger rather than faked or
quietly dropped: without it, a constant ANCHOR alongside a live
revision still passes every terminal row that exists.

The two test hooks are `#[doc(hidden)] pub`, not `#[cfg(test)]`,
because the rows needing them are integration tests and those link the
library without `cfg(test)`.

Verified: focused suite 37/37, `cargo test --lib` 1945 green, clippy
clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai

docs/active-work.md

@@ -437,6 +437,17 @@ from #171 and #215.
     three of them lost to these two signatures. U9's synthetic-load
     control remains unrun and is the cheapest thing that would either
     implicate load or clear it.
+- **OWED WITNESS — terminal scroll-anchor movement at the daemon
+  level.** The anchor is in the key (`PanelMappingContent::Terminal`
+  carries it) and the review asked for a row proving the daemon's
+  generation moves when it does. **Three attempts failed to drive a
+  scroll from the panel fixture**: `scroll_lines` needs a viewport the
+  panel projection registers on its own schedule, and `scroll_view`
+  with an explicit content size still reports no movement after forty
+  line feeds, so the history it would move into is not accumulating as
+  the fixture assumes. **Recorded rather than faked.** Without it, a
+  `view_mapping_identity` returning a constant ANCHOR while reporting a
+  live revision passes every terminal row that exists.
 - **Gates:** the four `bottom_panel_*` suites, the GUI 1a wire suite,
   `PMACS_REQUIRE_GPU=1 cargo test -p pmacs-gpu`, and **`--protocol`**.
 

src/editor.rs

@@ -396,12 +396,6 @@ pub struct PanelMappingSnapshot {
     /// inverts nothing like a 6×2 one.
     rows: u32,
     cols: u32,
-    view_top: usize,
-    view_left: u32,
-    wrap: crate::view::WrapMode,
-    content_cols: u32,
-    fold_projection: bool,
-    folds: Vec<pmacs_protocol::ByteRange>,
     content: PanelMappingContent,
 }
 
@@ -422,6 +416,18 @@ pub enum PanelMappingContent {
     Document {
         /// The buffer's content revision, or `None` if it is gone.
         revision: Option<u64>,
+        /// Vertical viewport origin.
+        view_top: usize,
+        /// Horizontal viewport origin. GUI arc 1b makes this move.
+        view_left: u32,
+        /// Wrap mode: it decides how a source line becomes display rows.
+        wrap: crate::view::WrapMode,
+        /// Text width with the gutter reservation already subtracted.
+        content_cols: u32,
+        /// The owning frontend's fold projection policy.
+        fold_projection: bool,
+        /// Fold content, read at its source.
+        folds: Vec<pmacs_protocol::ByteRange>,
     },
     /// A terminal panel: the screen's **mapping revision** and the
     /// view's scroll anchor.
@@ -2545,13 +2551,8 @@ impl EditorState {
                 .get(buffer_id)
                 .ok()
                 .map(crate::buffer::Buffer::revision);
-            PanelMappingContent::Document { revision }
+            PanelMappingContent::Document {
-        };
+                revision,
-
-        Some(PanelMappingSnapshot {
-            buffer_id,
-            rows: size.rows,
-            cols: size.cols,
                 view_top: window.view_top,
                 view_left: window.view_left,
                 wrap: window.last_wrap,
@@ -2560,12 +2561,23 @@ impl EditorState {
                     .views
                     .get(&frontend_id)
                     .is_some_and(|view| view.fold_projection),
-            // Read at their SOURCE — the registry's ranges — rather than
+                // Read at their SOURCE — the registry's ranges — rather
-            // through the derived `VisibleLineMap`, whose only public
+                // than through the derived `VisibleLineMap`, whose only
-            // summary is `is_identity()`. That is too coarse: a fold edit
+                // public summary is `is_identity()`. Too coarse: a fold
-            // leaving the map non-identity still changes which source
+                // edit leaving the map non-identity still changes which
-            // line a row shows.
+                // source line a row shows.
                 folds: core.fold_registry.folds(buffer_id),
+            }
+        };
+
+        // Only COMMON geometry lives out here. Everything below is
+        // domain-specific: `view_top`, `view_left`, wrap, gutter width
+        // and folds describe a DOCUMENT projection and take no part in a
+        // terminal's, where the child's screen decides the mapping.
+        Some(PanelMappingSnapshot {
+            buffer_id,
+            rows: size.rows,
+            cols: size.cols,
             content,
         })
     }

src/terminal/screen.rs

@@ -114,6 +114,15 @@ pub struct ScreenProjection {
     pub title: Option<String>,
     /// Screen generation represented by this projection.
     pub generation: u64,
+    /// §5b — the **mapping revision** this projection was published at.
+    ///
+    /// Carried here, not read live, because the two diverge while
+    /// synchronized output is held: `projection_ref` keeps returning the
+    /// last PUBLISHED cells while the live screen races ahead, so
+    /// stamping a frame with the live revision would give displayed
+    /// cells authority they were never painted under — a frontend would
+    /// then echo a generation that matches nothing it can see.
+    pub mapping_revision: u64,
 }
 
 /// Borrowed, publication-consistent row projection for in-process views.
@@ -128,6 +137,8 @@ pub(crate) struct BorrowedScreenProjection<'a> {
     pub cursor: Option<CellCoord>,
     pub title: Option<&'a str>,
     pub generation: u64,
+    /// §5b — the mapping revision this projection was published at.
+    pub mapping_revision: u64,
 }
 
 impl BorrowedScreenProjection<'_> {
@@ -147,6 +158,7 @@ impl ScreenProjection {
             cursor: self.cursor,
             title: self.title.as_deref(),
             generation: self.generation,
+            mapping_revision: self.mapping_revision,
         }
     }
 }
@@ -224,6 +236,7 @@ impl TerminalScreen {
             cursor: Some(CellCoord::new(0, 0)),
             title: None,
             generation: 0,
+            mapping_revision: 0,
         };
         Ok(Self {
             size,
@@ -599,6 +612,7 @@ impl TerminalScreen {
                 .then(|| CellCoord::new(self.cursor.row as u32, self.cursor.col as u32)),
             title: self.title.as_deref(),
             generation: self.generation,
+            mapping_revision: self.mapping_revision,
         }
     }
 
@@ -658,7 +672,7 @@ impl TerminalScreen {
         self.g0 = saved.g0;
         self.g1 = saved.g1;
         self.use_g1 = saved.use_g1;
-        self.changed();
+        self.display_only_changed();
     }
 
     fn write_text(&mut self, text: &str) {
@@ -812,6 +826,24 @@ impl TerminalScreen {
         if self.modes.insert {
             self.insert_characters(width as u32);
         }
+        // §5b — did the GLYPH change, or only the pen? Rewriting the
+        // same character in a new colour repaints the cell without
+        // changing what the coordinate denotes, and a drag must survive
+        // it.
+        //
+        // Sampled BEFORE `clear_wide_at`, which blanks the cell when it
+        // is part of a wide pair — sampling after would compare the new
+        // glyph against a default and call every rewrite a change.
+        let glyph_changed = {
+            let row = self.cursor.row;
+            let col = self.cursor.col;
+            let cells = &self.active().rows[row].cells;
+            cells[col].glyph != Glyph::Char(ch)
+                || (width == 2
+                    && cells
+                        .get(col + 1)
+                        .is_none_or(|next| next.glyph != Glyph::Continuation))
+        };
         self.clear_wide_at(self.cursor.row, self.cursor.col);
         if width == 2 {
             self.clear_wide_at(self.cursor.row, self.cursor.col + 1);
@@ -832,7 +864,11 @@ impl TerminalScreen {
             self.cursor.pending_wrap = false;
         }
         self.last_grapheme = Some((row, col));
+        if glyph_changed {
             self.changed();
+        } else {
+            self.display_only_changed();
+        }
     }
 
     fn soft_wrap(&mut self) {
@@ -886,7 +922,7 @@ impl TerminalScreen {
             .copied()
             .unwrap_or(cols - 1);
         self.cursor.pending_wrap = false;
-        self.changed();
+        self.display_only_changed();
     }
 
     fn move_vertical(&mut self, delta: i64) {
@@ -903,7 +939,7 @@ impl TerminalScreen {
         };
         self.cursor.row = moved.clamp(lo, hi);
         self.cursor.pending_wrap = false;
-        self.changed();
+        self.display_only_changed();
     }
 
     fn move_horizontal(&mut self, delta: i64) {
@@ -915,13 +951,13 @@ impl TerminalScreen {
         };
         self.cursor.col = moved.min(self.size.cols as usize - 1);
         self.cursor.pending_wrap = false;
-        self.changed();
+        self.display_only_changed();
     }
 
     fn set_col(&mut self, col: u32) {
         self.cursor.col = col.saturating_sub(1).min(self.size.cols - 1) as usize;
         self.cursor.pending_wrap = false;
-        self.changed();
+        self.display_only_changed();
     }
     fn set_row(&mut self, row: u32) {
         let base = if self.modes.origin {
@@ -936,7 +972,7 @@ impl TerminalScreen {
         };
         self.cursor.row = (base + row.saturating_sub(1) as usize).min(hi);
         self.cursor.pending_wrap = false;
-        self.changed();
+        self.display_only_changed();
     }
     fn set_position(&mut self, row: u32, col: u32) {
         self.set_row(row);
@@ -1525,8 +1561,20 @@ impl TerminalScreen {
                 .then(|| CellCoord::new(self.cursor.row as u32, self.cursor.col as u32)),
             title: self.title.clone(),
             generation: self.generation,
+            mapping_revision: self.mapping_revision,
         }
     }
+    /// Publish the current projection, for tests that drive events
+    /// directly instead of through the PTY reader.
+    ///
+    /// `#[doc(hidden)]` rather than `#[cfg(test)]`: the rows that need
+    /// it are integration tests, which link the library WITHOUT
+    /// `cfg(test)` and so cannot see a gated item.
+    #[doc(hidden)]
+    pub fn publish_for_test(&mut self) {
+        self.publish();
+    }
+
     fn publish(&mut self) {
         self.published = self.current_projection();
     }

src/terminal/view.rs

@@ -249,6 +249,34 @@ impl TerminalManager {
         self.screen_size(key.buffer_id)
     }
 
+    /// Apply one parsed event to a session's screen, for tests.
+    ///
+    /// Terminal output normally arrives on the PTY reader thread, which
+    /// no daemon-level test can drive deterministically. §5b's terminal
+    /// rows must nevertheless be witnessed **across the seam** — the
+    /// screen counter and the daemon's key are separately provable, and
+    /// a `view_mapping_identity` returning a constant would leave both
+    /// green — so this exists to join them.
+    ///
+    /// `#[doc(hidden)]` rather than `#[cfg(test)]`, because the rows
+    /// that need it are integration tests and those link the library
+    /// without `cfg(test)`.
+    #[doc(hidden)]
+    pub fn apply_event_for_test(
+        &mut self,
+        buffer_id: BufferId,
+        event: crate::ansi::AnsiEvent,
+    ) -> bool {
+        match self.sessions.get_mut(&buffer_id) {
+            Some(session) => {
+                session.screen.apply_event(event);
+                session.screen.publish_for_test();
+                true
+            }
+            None => false,
+        }
+    }
+
     /// §5b — the terminal's **mapping revision** plus its per-view
     /// scroll anchor: together, the identity of what a coordinate in
     /// this view denotes.
@@ -265,7 +293,14 @@ impl TerminalManager {
         // `top` IS the anchor: `None` means following the live tail,
         // which is itself a distinct state from any pinned row.
         let anchor = self.views.get(&key).and_then(|view| view.top);
-        Some((session.screen.mapping_revision(), anchor))
+        // The PUBLISHED revision, not the live one. While synchronized
+        // output is held, `projection_ref` keeps returning the last
+        // published cells while the screen races ahead — reading
+        // `screen.mapping_revision()` there would stamp displayed cells
+        // with authority they were never painted under, and the frontend
+        // would echo a generation matching nothing it can see.
+        let published = session.screen.projection_ref().mapping_revision;
+        Some((published, anchor))
     }
 
     /// The shared screen's current size, read from the borrowed
@@ -984,6 +1019,7 @@ mod tests {
             cursor: None,
             title: Some("shell".into()),
             generation: 7,
+            mapping_revision: 0,
         }
     }
 
@@ -1264,6 +1300,7 @@ mod tests {
             cursor: None,
             title: None,
             generation: 2,
+            mapping_revision: 0,
         };
         let mut state = TerminalViewState {
             top: Some(LogicalCellAnchor {

tests/bottom_panel_stage2b_daemon_acceptance.rs

@@ -1744,3 +1744,89 @@ fn the_mapping_snapshot_picks_the_terminal_domain_for_a_terminal_panel() {
         );
     }
 }
+
+/// §5b — the terminal key **across the seam**.
+///
+/// `screen.rs` proves the counter classifies events correctly, and the
+/// row above proves the snapshot picks the terminal domain. Neither
+/// notices a `view_mapping_identity` that returns a CONSTANT: the
+/// classification is right, the branch is taken, and the daemon's key
+/// still never moves. These rows join the two halves.
+#[test]
+fn g2_g3_a_terminal_panels_key_tracks_its_screen_and_anchor() {
+    use pmacs::ansi::AnsiEvent;
+
+    let mut session = Session::new();
+    session.declare(1, 24, 80);
+    exec(
+        &session.state,
+        "TERM_BUF = pmacs.terminal.open { command = \"/bin/sh\", \
+           args = { \"-c\", \"sleep 30\" }, display = \"panel\" }",
+    );
+    let _ = session.frame();
+
+    let buffer_id = {
+        let core = session.state.core.borrow();
+        let side = core.side_window_for(FID).expect("side");
+        core.windows[&side].buffer_id
+    };
+    let feed = |session: &Session, event: AnsiEvent| {
+        assert!(
+            session
+                .state
+                .terminal_manager
+                .borrow_mut()
+                .apply_event_for_test(buffer_id, event),
+            "the panel's terminal session must exist"
+        );
+    };
+
+    let start = mapping_generation(&mut session).expect("a terminal panel has a key");
+
+    // CHANGING: a glyph appears where none was.
+    feed(&session, AnsiEvent::Text("A".to_owned()));
+    let after_glyph = mapping_generation(&mut session).expect("a key");
+    assert!(
+        after_glyph > start,
+        "new output changes what a coordinate denotes"
+    );
+
+    // STABLE: the same glyph rewritten under a different pen. This is
+    // the row that forced `write_character` to compare glyphs — a
+    // blanket bump made a recolour cancel the drag.
+    feed(&session, AnsiEvent::CursorPosition { row: 1, col: 1 });
+    feed(
+        &session,
+        AnsiEvent::SetStyle(pmacs_protocol::Style::default()),
+    );
+    feed(&session, AnsiEvent::Text("A".to_owned()));
+    assert_eq!(
+        mapping_generation(&mut session),
+        Some(after_glyph),
+        "rewriting the SAME glyph in another style repaints the cell \
+         without moving what it denotes"
+    );
+
+    // STABLE: ordinary cursor motion.
+    feed(&session, AnsiEvent::CursorPosition { row: 2, col: 3 });
+    assert_eq!(
+        mapping_generation(&mut session),
+        Some(after_glyph),
+        "moving the caret denotes nothing new — and these paths were \
+         advancing the revision until §5b's terminal correction"
+    );
+
+    // NOT YET WITNESSED: scroll-anchor movement at this level.
+    //
+    // The anchor IS in the key — `PanelMappingContent::Terminal` carries
+    // it — but driving a scroll from here has defeated three attempts:
+    // `scroll_lines` needs a viewport the panel projection registers on
+    // its own schedule, and `scroll_view` with an explicit size still
+    // reports no movement after forty line feeds, so the history the
+    // scroll would move into is not accumulating the way this fixture
+    // assumes.
+    //
+    // Recorded as OWED rather than faked. Without it, a
+    // `view_mapping_identity` that returned a constant ANCHOR while
+    // reporting a live revision would pass every row above.
+}