A single 'hermes update' / 'hermes -p' could rewrite a hand-curated config.yaml
into a near-full DEFAULT_CONFIG dump (the 'you blow up my profile config on one
tweak' reports). Root cause: migrate_config() had ~16 independent save_config()
call sites, each author deciding ad hoc whether to materialise a value, and many
persisted pure schema defaults with strip_defaults=False. Defaults already merge
transparently at read time via load_config(), so writing them is pure bloat that
also shadows future default changes (see save_config's docstring).
Architectural fix (not a per-site patch): introduce a single _persist_migration()
chokepoint that enforces one invariant — a migration may persist only values that
DIFFER from the current schema default, plus explicit removals/renames of user
data; pure defaults are never written. Every migration write (all 17 sites incl.
the version-bump finalizer) now routes through it. The invariant is mechanically
correct for all cases and verified empirically:
- pure-default seeds (timezone='', curator/auxiliary.curator blocks, interim
flag, curator.consolidate=False, empty plugins.enabled) are stripped → merged
in at read time;
- non-default values (write_approval=True, model_catalog.ttl_hours=1) preserved
via explicit-raw-path preservation;
- behaviour flips (agent.verify_on_stop=False, schema default still 'auto')
preserved because False != 'auto';
- data transforms (custom_providers->providers, stt.model relocation,
write_mode->write_approval, compression.summary_* removal, MCP-disable)
persist their removals/renames.
An explicitly user-set non-default value (e.g. matrix.require_mention: false) is
preserved across the bump.
Guard tests lock the architecture: an AST check asserts migrate_config() makes no
direct save_config() call (all writes go through _persist_migration), and a
full-range v1->latest test asserts a lean config is never dumped. Two existing
change-detector tests that froze the on-disk representation of default-valued
keys are rewritten to assert the effective value via load_config() (behaviour
contract, not snapshot).
Validation: lean v1->latest migration drops from ~567 bytes to ~196 bytes;
148 config+setup and 196 profile/curator/migrate tests pass on scripts/run_tests.sh.
kshitijk4poor
c717be8ded