Provenance and independence boundary

PiperG2P is independently implemented under Apache-2.0. Its compatibility requirements are based on public Piper configuration/behavior observations, the public eSpeak NG API, and documented optional adapter contracts. This page records the engineering provenance concisely; it is not a claim that the intentional espeakng-runtime dependency is absent.

Requirement	Public or behavioral basis	Independent implementation decision
Voice-specific ID maps	Piper voice configuration	Keep the loaded map authoritative and validate IDs locally.
BOS/PAD/EOS framing	Observed frontend behavior	Implement a small codec strategy without a universal map.
NFD normalization	Compatibility requirement	Use Python `unicodedata` at the frontend boundary.
Clause terminators	eSpeak NG public API and runtime contract	Use the `espeakng-runtime` public clause API and convert results at the Piper adapter boundary.
Native global-state locking	eSpeak public API behavior	Delegate process-wide locking and lifetime to `espeakng-runtime`.
Raw blocks	Observed Piper/eSpeak behavior	Use an independent state-machine parser and composition helper.
CLI fallback	Existing frontend behavior	Delegate CLI execution to `espeakng-runtime`, retaining Piper-local splitting and composition.
Lexphon managed assets	Lexphon public data/profile APIs	Keep installation and verification external; interpret assets in the optional adapter.
G2Lex local assets	G2Lex public open/lookup APIs	Keep direct lookup narrow, ordered, and exact-key.
Sibling architecture	Public API conventions	Reuse lifecycle ideas without copying source or tests.

Built-in lexicon adapters preserve phoneme_encoding, lexicon ID, data version, producer, transform, and generator identity. Generic ipa is an override; espeak-ipa3 represents Piper raw pronunciation content.

The PiperG2P package does not import the Piper runtime/package or bundle Piper source, tests, lookup tables, models, or resources. espeakng-runtime is an intentional runtime dependency for eSpeak infrastructure. Pinned upstream identity in benchmark metadata is historical evidence, not code to port.

eSpeak-derived test assets are generated during tests from declared source words and pronunciations. Production dictionaries are not bundled for test convenience.