Descend into a task with the same bookkeeping as an ordinary callsite

[jishnub]

The TaskCallInfo branch in descend! sets state.ci alone:

state.ci = get_ci(info)::CodeInstance
descend!(state)
continue

Two consequences:

• state.mi stays the parent's. Every view reads state.mi — get_typed_sourcetext(state.mi, …) for :source, state.mi.def for :ast and jump, and the (state.mi, result.src) pair handed to _dump_function for :llvm/:native — so descending into a task renders the parent's method with the task's code, and hands codegen a mismatched pair.
• Nothing restores the parent's state on the way back up, so after ascending the parent's frame keeps the task's ci.

This makes the branch do what the ordinary descent a few lines below already does: save the state, set mi with ci, clear override, descend, honour :exited, restore.

Test (terminal harness): descending into the task callsite of @sync @async show(devnull, "Hello") shows the closure's method as the frame header, and ascending brings back the parent's header and its own callsites. Against master the test fails on all three of those assertions.

Not changed: get_ci(info)::CodeInstance still throws when the task wraps a MultiCallInfo (which callinfo() can return). That is a separate question of what the TUI should offer there.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NiXhCrQf5AJ2DmTmZ3FsSP

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (2c33b9a) to head (db17250).
⚠️ Report is 101 commits behind head on master.

Files with missing lines	Patch %	Lines
src/descend.jl	0.00%	10 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #709    +/-   ##
=======================================
  Coverage    0.00%   0.00%            
=======================================
  Files           9      22    +13     
  Lines        1556    1816   +260     
=======================================
- Misses       1556    1816   +260     

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