Builds on webtecnica's escape-aware _split_key_path (#84152, cherry-picked
with authorship preserved; earliest fix in the family was RelaxJonh's #80253
greedy-match approach — both behaviors now ship together):
- _greedy_literal_match: when navigating an EXISTING mapping, prefer an
existing literal key equal to the dot-join of the next N path segments
(longest match wins). Dotted model IDs are the norm, so the common
unescaped command (config set providers.p.models.grok-4.6.supports_vision
true) now hits the real key across set/get/unset instead of creating a
phantom sibling. Plain dotted paths with no dotted-key collision split
exactly as before.
- _phantom_sibling + ValueError in _set_nested: refuse to CREATE a new
intermediate mapping that would shadow an existing dotted literal sibling
(Soju06's fail-loudly suggestion on #84064); set_config_value surfaces it
as a clean CLI error with the escaped spelling to use.
- utils.py::atomic_roundtrip_yaml_update (the second split site, #91607 —
/model + TUI persistence) now uses the same escape-aware split + greedy
literal matching.
- CFG-04 empty-segment guard now splits escape-aware so escaped keys are
not misclassified.
- Tests for every repro shape in the family: #84064 provider model keys,
#80006 Matrix room IDs, #91095 dotted models under custom_providers list
index (incl. escaped creation-when-absent), #91607 model_overrides via
atomic_roundtrip_yaml_update, #99124 dotted leaf keys; plus
backward-compat coverage. Also fixed the carrier's one stale assertion
(structured-value coercion landed on main after #84152 branched) and
removed its dead _MCP_SECRETS_CONFIG fixture flagged in review.
- Docs: 'Dots inside key names' section in website/docs/reference/cli-commands.md.
Fixes#84064, fixes#80006, fixes#91095, fixes#91607, fixes#99124
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