trace: stepping stays in the view you're reading

Caught while demoing this in a live pane, not by a test: press Tab to read the
pseudocode, press ] once, and you're back in the disassembly.

_seek() follows the trace by navigating to the new PC, and navigating to an
ADDRESS opens the listing unless the decompiler is explicitly preferred. So
every step out of C dropped you out of C — the painting work of the last commit
was unusable in the view it was built for, from the first keypress.

_seek now passes prefer_decomp=(self._active == "decomp"), the same thing the
xref handler already does for the same reason.

Worth noting what it looks like when it works: stepping in pseudocode follows
execution INTO a callee and the view switches to that function's C, which is
what you want and what makes the decompiler painting worth having.

tests: +2 trace UI (23) asserting the view survives a step in both directions.
212/0 scenarios.

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/test_trace_ui.py b/tests/test_trace_ui.py
index a85c089..a43c11d 100644
--- a/tests/test_trace_ui.py
+++ b/tests/test_trace_ui.py
@@ -194,6 +194,20 @@ async def run() -> int:
                       t.ip(app._t) in covered,
                       f"pc={t.ip(app._t):#x} line covers {[hex(a) for a in covered][:4]}")
 
+                # Stepping must not throw you out of the view you're reading.
+                # A step navigates to an address, and navigating to an address
+                # opens the LISTING unless the decompiler is preferred — so
+                # stepping through C used to drop you into disassembly on the
+                # first keypress. Found by watching a demo, not by a test.
+                await pilot.press("]")
+                await pilot.pause(1.2)
+                check("stepping in pseudocode stays in pseudocode",
+                      app._active == "decomp", f"active={app._active}")
+                await pilot.press("[")
+                await pilot.pause(1.2)
+                check("and so does stepping backward",
+                      app._active == "decomp", f"active={app._active}")
+
     print(f"\n{PASS} passed, {FAIL} failed")
     return 1 if FAIL else 0