contents_processor.go missing isConfirmationEvent filter breaks tool confirmation with persistent session stores

[odsod]

🔴 Required Information

Describe the Bug:

buildContentsDefault in internal/llminternal/contents_processor.go filters adk_request_credential events from LLM history via isAuthEvent(), but has no equivalent filter for adk_request_confirmation events. When using a persistent session store (anything other than InMemorySessionService), confirmation events are replayed into the Gemini context on the next turn, causing a 400 error because Gemini sees FunctionCall/FunctionResponse parts for adk_request_confirmation — a function it never declared.

This is documented as a known limitation in docs/tools-custom/confirmation.md:

Known limitations:

• DatabaseSessionService is not supported by this feature.
• VertexAiSessionService is not supported by this feature.

The fix below removes this limitation.

Steps to Reproduce:

1. Configure an agent with a tool that uses ctx.RequestConfirmation() (or RequireConfirmation: true)
2. Use any persistent SessionService (database-backed, custom implementation, etc.)
3. User sends a message that triggers the tool → confirmation event is stored in session
4. User sends confirmation response (FunctionResponse with adk_request_confirmation)
5. RequestConfirmationRequestProcessor re-executes the tool and yields the result
6. ContentsRequestProcessor builds LLM history from session — includes adk_request_confirmation events
7. Gemini returns 400: "Please ensure that the number of function response parts is equal to the number of function call parts of the function call turn"

Expected Behavior:

adk_request_confirmation events should be filtered from LLM history, matching the existing isAuthEvent() pattern for adk_request_credential.

Observed Behavior:

Gemini 400 error on the confirmation response turn. Tool confirmation only works with InMemorySessionService.

Proposed Fix:

Add isConfirmationEvent() filter in buildContentsDefault, mirroring isAuthEvent():

// In buildContentsDefault, after isAuthEvent check:
if isConfirmationEvent(ev) {
    continue
}

// New function:
const requestConfirmationFunctionCallName = "adk_request_confirmation"

func isConfirmationEvent(ev *session.Event) bool {
    c := utils.Content(ev)
    if c == nil {
        return false
    }
    for _, p := range c.Parts {
        if p.FunctionCall != nil && p.FunctionCall.Name == requestConfirmationFunctionCallName {
            return true
        }
        if p.FunctionResponse != nil && p.FunctionResponse.Name == requestConfirmationFunctionCallName {
            return true
        }
    }
    return false
}

Environment Details:

• ADK Library Version: v1.0.0
• OS: Linux
• Go Version: 1.26

Model Information:

• Gemini 2.5 Flash / Pro (any model — the issue is in event history construction, not model-specific)

---

🟡 Optional Information

Related Issues:

• Missing ThoughtSignature on adk_request_confirmation parts breaks execution #656 (ThoughtSignature missing on confirmation events — different bug, same flow)
• generateRequestConfirmationEvent creates events with missing ID #590, generateRequestConfirmationEvent creates events with empty ID, causing DB primary key violations #558 (confirmation event missing ID — different bug, same flow)

How often has this issue occurred?:

Always (100%) — deterministic when using persistent sessions with tool confirmation.