[Repo Assist] fix(config): wire payloadSizeThreshold in JSON stdin + add keepaliveInterval to schema

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Fixes three compliance gaps identified in #3272 (Daily Compliance Review 2026-04-06).

What

1. keepaliveInterval rejected by JSON schema (spec §4.1.3.5)

The embedded schema (v0.64.4) did not include keepaliveInterval in gatewayConfig.properties, causing schema validation to reject it with additionalProperties: false. The Go struct StdinGatewayConfig.KeepaliveInterval already existed — only the schema was wrong.

Fix: Register keepaliveInterval in fixSchemaBytes alongside trustedBots, using the same dynamic-addition pattern.

2. payloadSizeThreshold silently ignored in JSON stdin (spec §4.1.3.3)

The embedded schema correctly listed payloadSizeThreshold in gatewayConfig.properties, so validation passed — but StdinGatewayConfig had no PayloadSizeThreshold field. Go's JSON unmarshaler silently dropped the value.

Fix: Add PayloadSizeThreshold *int to StdinGatewayConfig and wire it in convertStdinConfig.

3. Negative payload_size_threshold not rejected in TOML path (spec §4.1.3.3)

applyDefaults replaced 0 with the default, but a negative value like -1 passed all validation and would silently cause every payload to be stored to disk.

Fix: After applyDefaults, reject any negative PayloadSizeThreshold in ParseConfig.

A validation check for the JSON stdin path (in validateGatewayConfig) also ensures payloadSizeThreshold is positive when provided.

Changes

File	Change
internal/config/validation_schema.go	Register keepaliveInterval in fixSchemaBytes
internal/config/config_stdin.go	Add PayloadSizeThreshold *int to StdinGatewayConfig; wire in convertStdinConfig
internal/config/validation.go	Validate payloadSizeThreshold >= 1 in JSON stdin path
internal/config/config_core.go	Validate PayloadSizeThreshold >= 0 in TOML path
internal/config/config_stdin_test.go	Tests for wiring and validation
internal/config/config_core_test.go	Test for negative TOML value rejection
internal/config/validation_schema_test.go	Tests that keepaliveInterval is now accepted

Test Status

⚠️ Infrastructure limitation: Go 1.25.0 is not available in the agent environment (network download blocked). Tests cannot be executed locally.

The changes are straightforward struct field additions, wiring, and a bounds check. All logic is covered by new unit tests that will run in CI.

CI will verify all three fixes via the new tests added to config_stdin_test.go, config_core_test.go, and validation_schema_test.go.

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[Copilot]

Pull request overview

This PR addresses MCP Gateway spec-compliance gaps in config handling by aligning JSON stdin parsing/validation and the embedded JSON schema with supported gateway config fields, and by rejecting invalid payload threshold values in the TOML load path.

Changes:

• Extend the embedded JSON schema fix-up to allow keepaliveInterval in gateway configs.
• Add payloadSizeThreshold support to JSON stdin (StdinGatewayConfig) and wire it into the internal GatewayConfig.
• Add validation to reject invalid payloadSizeThreshold (JSON stdin) and negative payload_size_threshold (TOML).

Show a summary per file

File	Description
internal/config/validation.go	Adds JSON-stdin validation for payloadSizeThreshold >= 1.
internal/config/validation_schema.go	Dynamically injects keepaliveInterval into the embedded schema.
internal/config/validation_schema_test.go	Adds schema acceptance tests for keepaliveInterval (incl. -1).
internal/config/config_stdin.go	Adds PayloadSizeThreshold to stdin config and maps it into GatewayConfig.
internal/config/config_stdin_test.go	Adds tests for stdin wiring and validation of payloadSizeThreshold.
internal/config/config_core.go	Rejects negative payload_size_threshold values after defaults are applied.
internal/config/config_core_test.go	Adds a TOML test ensuring negative payload_size_threshold is rejected.

Copilot's findings

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• Files reviewed: 7/7 changed files
• Comments generated: 2

[Copilot]

The newly added schema description says “0 or unset for gateway default (1500s)”, but in the JSON stdin path a user-provided keepaliveInterval=0 will be preserved (intPtrOrDefault returns 0) and GatewayConfig.HTTPKeepaliveInterval() converts 0 to a 0s duration (effectively disabling keepalive). This makes the schema/docs misleading and creates inconsistent behavior vs TOML (where 0 is normalized to the default). Consider either (a) treating 0 as unset/default during stdin conversion or validation, or (b) updating the schema description (and any related docs) to reflect that 0 disables keepalive and only nil uses the default.

Suggested change

	"description": "Keepalive ping interval in seconds for HTTP MCP backends. Use -1 to disable, 0 or unset for gateway default (1500s), or a positive integer for a custom interval.",
	"description": "Keepalive ping interval in seconds for HTTP MCP backends. Use -1 to disable, unset for the gateway default (1500s), 0 to disable HTTP keepalive, or a positive integer for a custom interval.",

[Copilot]

This change makes payloadSizeThreshold configurable via JSON stdin, but docs/CONFIGURATION.md currently lists “Payload size threshold” under “TOML-only / CLI-only options (not available in JSON stdin)”. Please update the documentation (and any related references) so users know the field is now supported in JSON stdin and what its JSON name is (payloadSizeThreshold).

See below for a potential fix:

	Port           *int   `json:"port,omitempty"`
	APIKey         string `json:"apiKey,omitempty"`
	Domain         string `json:"domain,omitempty"`
	StartupTimeout *int   `json:"startupTimeout,omitempty"`
	ToolTimeout    *int   `json:"toolTimeout,omitempty"`

	// KeepaliveInterval configures the keepalive interval in JSON stdin as `keepaliveInterval`.
	KeepaliveInterval *int `json:"keepaliveInterval,omitempty"`

	// PayloadDir configures the payload directory in JSON stdin as `payloadDir`.
	PayloadDir string `json:"payloadDir,omitempty"`

	// PayloadSizeThreshold configures the payload size threshold in JSON stdin as
	// `payloadSizeThreshold`.
	PayloadSizeThreshold *int `json:"payloadSizeThreshold,omitempty"`

	// TrustedBots configures trusted bot identifiers in JSON stdin as `trustedBots`.
	TrustedBots []string `json:"trustedBots,omitempty"`

	OpenTelemetry *StdinOpenTelemetryConfig `json:"opentelemetry,omitempty"`