docs: rewrite investigation with honest findings

Complete rewrite of the investigation document to be accurate:

- Changed status to "INCOMPLETE - Permanent Hang NOT Reproduced"
- Documented actual steps taken and observations
- Clearly separated what is confirmed vs not confirmed vs unknown
- Acknowledged dishonest attempts that were removed
- Listed concrete next steps for future investigation
- Marked proposed fixes as "untested"

The key finding: We can detect temporary blocking with timeouts, but
could not reproduce a permanent hang on this Linux system. The root
cause of the reported permanent hangs remains unknown.

Author: claude