fix(google): drop unsupported JSON Schema keywords before validating

[feiiiiii5]

Problem

Any MCP tool whose JSON Schema carries a legal annotation keyword — readOnly, deprecated, $comment, x-google-enum-descriptions, or any other vendor extension — makes the Gemini Realtime session fail to build its tool declarations. The worker joins the room, publishes its mic track, and then never speaks, because the schema was rejected before the session could start.

_GeminiJsonSchema._simplify removes a fixed list of keywords it knows Gemini does not accept (title, default, additionalProperties, $schema, discriminator, examples, and const, which is folded into enum). Everything else is passed through untouched and ends up in:

types.FunctionDeclaration.model_validate({"name": ..., "parameters": params})

types.Schema is declared with extra="forbid", so the first keyword outside that fixed list raises a ValidationError. The list is a deny-list against a model that validates by allow-list, so it cannot stay in sync.

Concretely, on main (e5024c7), a schema containing "readOnly": True produces:

pydantic_core._pydantic_core.ValidationError: 1 validation error for FunctionDeclaration
parameters.properties.attachments.items.properties.id.readOnly
  Extra inputs are not permitted [type=extra_forbidden, input_value=True, input_type=bool]

Fix

Derive the accepted keyword set from types.Schema.model_fields and its camelCase aliases, instead of maintaining a separate list that drifts, and prune at the top of _simplify so nested schemas and $defs/$ref targets are covered as well.

Three keys are added back explicitly because _simplify itself consumes them before the declaration is built: anyOf, $ref and prefixItems.

This keeps the existing behaviour for every keyword the transformer already understood, and only changes what happens to keywords it never handled.

Verification

livekit/agents at e5024c7, Python 3.13, macOS arm64, google-genai 2.24.0.

step	result
pytest tests/test_schema_gemini.py --unit at base, with the two new tests added	2 failed, 9 passed
same command with the fix	11 passed
pytest tests/test_google_thought_signatures.py tests/test_google_credentials.py tests/test_tools.py --unit	186 passed
ruff check <both files>	All checks passed
ruff format --check <both files>	2 files already formatted

The two added tests both fail on unmodified main and assert different halves of the fix: the first pins that an x-google-* extension and readOnly are gone from the output and that the declaration then validates; the second puts the unknown keyword inside a $defs entry reached through a $ref, which is the nested path the old deny-list never reached.

No network access and no API key is needed; the tests exercise _GeminiJsonSchema.simplify() directly and validate through types.FunctionDeclaration.

Scope note

There is a second, separate defect I did not fold in here: realtime_api.py:971 calls config = self._build_connect_config() outside the try: that starts on the next line, so any exception raised while building the config escapes the retry loop and the _emit_error handler below it. That is why this class of schema error is permanent rather than surfaced and retried. It is a distinct root cause in the session lifecycle, so I am leaving it to its own change rather than mixing a lifecycle fix into a schema fix.

AI assistance

AI-assisted development. An assistant helped locate the deny-list/extra="forbid" mismatch and draft the tests and this description. Every command result quoted above was run locally against e5024c7 before posting, including the failing-at-base run.

Refs #7349

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[devin-ai-integration]

Devin Review found 1 potential issue.

[devin-ai-integration]

🟡 Const constraints are silently removed

Schemas containing const lose it before the existing enum conversion runs. Literal-valued tool parameters then accept values outside their declared constant.

Learn more

const is a JSON Schema keyword that permits exactly one value. The transformer already converts it into Gemini's supported single-value enum at lines 173–175. The new allow-list removes const first, so that conversion becomes unreachable and the value restriction disappears. This affects generated schemas for single-value literals and tagged variants.

Example: A parameter schema {"type": "string", "const": "only"} previously became {"type": STRING, "enum": ["only"]}. It now becomes only {"type": STRING}, allowing Gemini to emit any string.

Recommended fix: Add const to _ALLOWED_KEYS, alongside the other keywords consumed by _simplify, so the existing conversion can preserve the constraint.

Suggested change

	| {"anyOf", "$ref", "prefixItems"}
	| {"anyOf", "$ref", "prefixItems", "const"}

---

Was this helpful? React with 👍 or 👎 to provide feedback.