Attach response output message IDs only to phased assistant messages

[dileepyavan]

Fixes microsoft/vscode#305838.

This change removes the redundant standalone response-output-message-id prompt path for OpenAI Responses API round-tripping and keeps that identifier attached only to phased assistant messages.

What changed:

• Moved responseOutputMessageId into phase metadata so phased assistant messages carry the phase and id together.
• Stopped attaching/sending a response output message id for non-phased assistant messages.
• Kept non-phased assistant history in the Responses API request body as plain assistant input messages.
• Simplified assistant prompt reconstruction to read the id from phase metadata instead of a separate opaque payload.
• Added regression coverage for the Responses API request body conversion.

Why:

• The output message id is only meaningful for assistant messages that are emitted with a phase.
• Keeping it separate added extra serialization and prompt plumbing for OpenAI model requests.
• Collapsing it into phase metadata reduces metadata overhead and simplifies the round-trip path.

Validation:

• npm run test:unit -- src/platform/endpoint/node/test/responsesApi.spec.ts
• TypeScript watch compile reported 0 errors

Notes:

• The generic streaming delta still exposes phase and responseOutputMessageId separately so provider-agnostic response handling remains unchanged.
• The simplification is applied in the persisted prompt metadata and resend path, which is where the redundant payload previously affected OpenAI Responses requests.

[Copilot]

Pull request overview

This PR simplifies OpenAI Responses API round-tripping by attaching the responseOutputMessageId only to phased assistant messages (stored alongside phase metadata), and stops emitting/sending that ID for non-phased assistant history.

Changes:

• Added responseOutputMessageId plumbing to streamed deltas and tool-calling round persistence.
• Moved Responses API request-body reconstruction to read the ID from phase metadata and emit IDs only for phased assistant messages.
• Added unit regression coverage for the Responses API request body conversion.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/platform/networking/common/fetch.ts	Extends IResponseDelta with responseOutputMessageId for round-tripping support.
src/platform/endpoint/node/responsesApi.ts	Emits message IDs only for phased assistant messages; non-phased assistant history becomes plain assistant input messages.
src/platform/endpoint/node/test/responsesApi.spec.ts	Adds regression test asserting IDs are only sent for phased assistant messages.
src/platform/endpoint/common/phaseDataContainer.tsx	Expands phase opaque payload to include responseOutputMessageId; adds encode/decode helpers for LM DataParts.
src/extension/prompts/node/panel/toolCalling.tsx	Includes responseOutputMessageId in PhaseDataContainer when rendering historical phased rounds.
src/extension/prompt/common/toolCallRound.ts	Persists responseOutputMessageId on ToolCallRound.
src/extension/prompt/common/intents.ts	Adds responseOutputMessageId to IToolCallRound.
src/extension/intents/node/toolCallingLoop.ts	Captures responseOutputMessageId from streaming deltas and stores it on the round.
src/extension/conversation/vscode-node/languageModelAccessPrompt.tsx	Decodes phase metadata from LM DataParts and re-embeds via PhaseDataContainer.
src/extension/conversation/vscode-node/languageModelAccess.ts	Encodes phase metadata (including output message id) into LM progress DataParts.

[hyperare80-pixel]

remove-