fix(embedded): preserve shell environment variables when constructor defaults are empty

[handnewb]

Summary

Fixes #3253: HindsightEmbedded constructor included every parameter in the config dict even when the caller left them at their default of "". Those empty-string values travelled through the daemon-startup env pipeline and overwrote the caller's actual shell environment variables set via export or .env files.

Root Cause

The HINDSIGHT_* propagation loop in _start_daemon (line 543) used value is not None as its guard:

An empty string ("") is not None, so it was always propagated and overwrote any prior os.environ value. The caller's HINDSIGHT_API_LLM_API_KEY from their shell was silently replaced with "".

Changes (defence in depth)

1. embedded.py — source fix

New _set_if_truthy helper: only adds keys with truthy values to the config dict. An empty default no longer poisons the merged env. This is the primary fix — the constructor never emits empty values in the first place.

2. daemon_embed_manager.py — defense in depth

Guard propagation on value (truthy) instead of value is not None. Even if an empty string reaches this loop through some other path, it is harmlessly skipped.

Impact

Users can now set HINDSIGHT_API_LLM_API_KEY (and every other HINDSIGHT_* var) in their shell environment and have HindsightEmbedded() pick it up without explicitly passing it to the constructor.