Follow-up to #2478 (merge commit e8f27c73).

The new AsyncLogWriter writes to a single timestamped log file (e.g. aethersdr-20260509-144822.log) that grows unbounded until process exit. On long-running operator sessions — contests, beacon monitoring, multi-day SmartLink leases — the log can grow to tens or hundreds of MB depending on category filtering. No size cap, no rotation.

This is pre-existing behavior, not introduced by #2478, but #2478 makes log throughput cheaper and therefore makes this concern more relevant in practice (more verbose categories enabled by default → faster disk fill).

Symptoms when it bites

• Disk space exhaustion on systems with small ~/.config partition or low free space
• aethersdr.log symlink points to a multi-GB file after a week-long session
• Support bundles become enormous and slow to upload
• macOS file system warnings about low free space on Library partition

Suggested approaches

A. Size-based rotation (simplest)

• New constant: kMaxLogFileSizeBytes = 50 * 1024 * 1024 (50 MB)
• Writer thread tracks file size after each batch
• When size exceeds limit: close current file, rename to .old, open new file with same name (or new timestamp), unlink any prior .old
• One .old file kept as backup; oldest discarded on next rotation

B. Time-based rotation

• New file every N hours (configurable, default 24h)
• Easier to reason about for support purposes ("give me yesterday's log")
• Filename naming continues the existing timestamp pattern

C. Hybrid (rotate on whichever happens first)

• Bounded by both size and age
• More complex but handles both "long quiet session" and "short verbose session" cleanly

D. AppSettings-controlled cap with cleanup-on-startup

• Setting: MaxLogFileSizeMb (default 100)
• Setting: LogRetentionDays (default 7)
• Cleanup loop on startup deletes timestamped logs older than retention or when total size exceeds cap
• No mid-session rotation; just bounded historical footprint

Considerations

• The aethersdr.log symlink (used by Support dialog) needs to follow rotation so support bundles capture the active file
• Active log file must be re-opened on rotation; AsyncLogWriter's writer thread is the only thread allowed to touch the file handle
• Rotation should never lose log lines — drain the buffer to the old file before swapping

Priority

Low. Disk-fill is a long-tail symptom; most operators don't keep AetherSDR running for days continuously. Worth doing as cleanup-on-startup at minimum (option D), as an opt-in setting, before any user actually hits a disk-full crash.

73, Jeremy KK7GWY & Claude (AI dev partner)