fix(openai): support Notion and Jira MCP tools with gpt-5 strict mode

[dgageot]

Problem

OpenAI's Responses API in strict mode (used by gpt-5/gpt-5.5 with Strict: true) requires additionalProperties to be literally false on every object schema. Some MCP servers ship tool schemas that violate this:

• Atlassian remote MCP (editJiraIssue): declares fields.additionalProperties: {} (or a richer schema). The request fails with:

  HTTP 400: Invalid schema for function 'atlassian-remote_editJiraIssue':
  In context=('properties', 'fields', 'additionalProperties'),
  'additionalProperties' is required to be supplied and to be false.
  

• Notion MCP (e.g. block-creation tools): declares additionalProperties as a schema (a map describing the dictionary value shape, like bulleted_list_item/numbered_list_item). Rewriting that to false would strip information the model relies on to call the tool correctly.

A previous fix overwrote schema-form additionalProperties with false everywhere — that fixed Jira but degraded Notion's tool calls.

Fix

Decide strict mode per tool:

1. ConvertParametersToSchema now returns (schema, strict, err).
2. A schema is strict-incompatible if any node has additionalProperties set to a map (schema form) or to true. We detect that with a read-only walk before any normalization.
3. Strict-compatible schemas go through the existing pipeline (makeAllRequired → forces additionalProperties: false, all properties required, nullables, etc.).
4. Strict-incompatible schemas are preserved (only cosmetic fixups: ensureTypeFields, removeFormatFields, fixSchemaArrayItems).
5. The Responses API tool definition uses Strict: param.NewOpt(strict) per tool.

Result:

• Jira's editJiraIssue works because we no longer claim strict mode on it.
• Notion's tools work because the inner dictionary schema survives the conversion.
• All other tools keep the existing strict-mode benefits.

Tests

• TestIsStrictCompatible covers strict, additionalProperties: true, and schema-form cases.
• TestConvertParametersToSchema_NotionStylePreservesShape proves Notion's inner schema is preserved end-to-end.
• TestMakeAllRequired_JiraEditIssueFields is a regression for the original Atlassian failure.
• All existing schema/conversion tests updated to the new 3-return signature.

Validation

• `go build ./...` ✅
• `go vet ./...` ✅
• `go test -race -count=1 ./pkg/model/provider/...` ✅
• `task lint` ✅ (0 issues)
• `go mod tidy --diff` clean ✅

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