diag: somewhere for swallowed errors to go

A TUI must not die because one background load failed, so this codebase catches
broadly -- ~50 `except Exception` sites, two dozen resolving to `pass`. Right
policy, one bad consequence: with 44 `@work(thread=True)` workers, a failure in
a background load leaves no trace whatsoever. The view stays empty and there is
nothing to read afterwards, because the app owns the screen.

kittygfx already solved this for itself with $IDATUI_KITTY_LOG. idatui/diag.py
is the same idea for everything else: $IDATUI_LOG writes every swallowed error
plus its traceback to a file, and the last 50 are kept in memory regardless so a
driver can ask a live app what went wrong. Unset, it costs an environ lookup.

Wired in where losing the error changes a DECISION rather than just a pixel:

  * rename: a resolve() that throws renames as DATA instead of as a function.
  * name: a function_of() that throws means we never learn the address is a
    function start, so the index keeps the old name and every readback says the
    rename didn't happen.
  * retype: a resolve() that throws retypes the ENCLOSING function instead.
  * decompile: a failed full-body fetch silently returns CLIPPED pseudocode.
  * trail: a failed decomp_map stops the pseudocode being painted, silently.

Deliberately NOT wired into the query_one guards -- a modal owning the screen is
normal and constant, and logging it would bury the real entries in noise.

New RPC verb `diag {n?, clear?}`, documented in docs/RPC.md: the answer to "the
verb reported success and the pane shows nothing".

Also a flake, same shape as the others: follow_xrefs waited on the nav depth but
asserted on _cur, and a follow pushes the source entry BEFORE opening the
target -- so the check could run in between and see the function it jumped
from. About one run in ten. It waits on the postcondition it asserts now; three
clean full runs since.

833 checks; --fast is 344 in 3.5s.

1 files changed, 6 insertions, 1 deletions

diff --git a/idatui/trace_ctl.py b/idatui/trace_ctl.py
index 46d4b17..8072801 100644
--- a/idatui/trace_ctl.py
+++ b/idatui/trace_ctl.py
@@ -21,6 +21,8 @@ import bisect
 import os
 from typing import TYPE_CHECKING
 
+from . import diag
+
 if TYPE_CHECKING:                                    # pragma: no cover
     from .app import IdaTui
 
@@ -264,7 +266,10 @@ class TraceController:
             # or twice, once for each of two parallel maps — would be felt.
             try:
                 app._apply_split_map(ea, app.program.decomp_map(ea))
-            except Exception:  # noqa: BLE001
+            except Exception as e:  # noqa: BLE001
+                # The pseudocode simply stops being painted with the trail, with
+                # nothing on screen to say why.
+                diag.note(f"trail: decomp_map({ea:#x})", e)
                 self.trail_map, self.trail_map_ea = [], ea
                 self.trail_line_of, self.trail_eas = {}, []
                 self.trail_span = None