fix: preserve only originally-required properties in strict tool schemas (#471)

Fixes #430. In normalizeSchemaForOpenAI(), the strict branch was adding every
property key to required[], including optional ones. This caused providers like
Groq, Azure OpenAI, and others to reject valid tool calls with a 400 /
tool_use_failed error because the model correctly omits optional arguments but
the provider sees them as missing required fields.

Root cause: the strict branch used `[...existingRequired, ...allKeys]` instead
of `existingRequired.filter(k => k in normalizedProps)`. The Gemini branch
already had the correct logic.

Fix: align the strict branch with the Gemini branch — only keep properties that
were already marked required in the original schema. The additionalProperties:
false constraint is preserved as strict-mode providers still require it.

Add regression test covering the Read tool schema (file_path required,
offset/limit/pages optional).

src/services/api/openaiShim.ts

@@ -421,11 +421,13 @@ function normalizeSchemaForOpenAI(
     record.properties = normalizedProps
 
     if (strict) {
-      // OpenAI strict mode requires every property to be listed in required[]
-      const allKeys = Object.keys(normalizedProps)
-      record.required = Array.from(new Set([...existingRequired, ...allKeys]))
-      // OpenAI strict mode requires additionalProperties: false on all object
-      // schemas — override unconditionally to ensure nested objects comply.
+      // Keep only the properties that were originally marked required in the schema.
+      // Adding every property to required[] (the previous behaviour) caused strict
+      // OpenAI-compatible providers (Groq, Azure, etc.) to reject tool calls because
+      // the model correctly omits optional arguments — but the provider treats them
+      // as missing required fields and returns a 400 / tool_use_failed error.
+      record.required = existingRequired.filter(k => k in normalizedProps)
+      // additionalProperties: false is still required by strict-mode providers.
       record.additionalProperties = false
     } else {
       // For Gemini: keep only existing required keys that are present in properties