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, 7 insertions, 2 deletions

diff --git a/tests/test_scenarios.py b/tests/test_scenarios.py
index 9934462..a36ea80 100644
--- a/tests/test_scenarios.py
+++ b/tests/test_scenarios.py
@@ -1362,11 +1362,16 @@ async def s_follow_xrefs(c: Ctx):
     orig_name = app._cur.name
     depth = len(app._nav)
     await c.press("enter")
-    await c.wait(lambda: len(app._nav) > depth, 25)
+    # Wait for exactly what the check asserts. Waiting only on the nav depth let
+    # the check run while _cur was still the function we jumped FROM -- the
+    # follow pushes the source entry before it opens the target -- so this
+    # failed about one run in ten with cur == orig, at full speed, looking like
+    # a code regression.
+    await c.wait(lambda: len(app._nav) > depth and app._cur.ea != orig, 25)
     c.check("Enter follows the call into another function",
             app._cur.ea != orig and len(app._nav) > depth, f"cur={app._cur.ea:#x}")
     await c.press("escape")
-    await c.pause(0.1)
+    await c.wait(lambda: app._cur.ea == orig, 15)
     c.check("Esc returns from the follow", app._cur.ea == orig, f"cur={app._cur.ea:#x}")
     dis.cursor = call_idx
     dis.refresh()