v2.1 minor breaking changes

Small, intentional changes to make the public API's names and data shapes more consistent. SDK consumers need to use the new fields. Existing stored data and old session imports remain readable through boundary decoders, without database migrations.

1. One name for provider replay data: native

Provider-owned data was called state, providerState or resultState depending on the message or event. These are now consistently named native, distinct from a tool's execution state and UI metadata.

The exported schema name SessionMessage.ProviderState also becomes SessionMessage.Native.

2. Tool call and result replay data share one tool.native

 tool
-  providerState?        # call data
-  providerResultState?  # result data
+  native?               # call + result data, shallow-merged
   state                 # execution status and readable output: unchanged

Success and failure events merge their native into the tool's existing native. Missing result data preserves call data; result values win on duplicate keys. There is no state.native.

Replay passes the whole merged blob to the protocol, which reads the fields it needs:

This avoids a second nested native, a one-off resultNative field, or a tool-specific { call, result } envelope. Protocol implementations must use distinct keys for distinct call/result values. Current Anthropic hosted calls carry no replay data; Responses hosted calls and results carry the same itemId.

Old stored/imported providerResultState is merged into tool.native when read. Tool status and readable result content stay in state.

3. Key credential form answers use metadata

 Credential.Key
   type: "key"
   key
   metadata?        # now also holds setup-form answers
-  configuration?   # setup-form answers (Form.Answer)

Credential.Key.configuration is removed. Setup-form answers now go in the existing metadata field, rather than keeping two bags of provider configuration. Stored credentials and auth import accept the old shape: a legacy configuration is merged into metadata, and the configuration value wins when both have the same key. Public credential writes must use metadata.

4. Compactions reference kept messages instead of storing recent

 summary compaction
-  recent: "[User]: ... [Assistant]: ..."
+  metadata: { keepID: "msg_..." }

keepID identifies the first message retained verbatim beside the summary. History reconstructs the text from that message through the compaction boundary, avoiding a duplicated, flattened copy in storage. Forks remap the reference to their copied messages; compaction hooks can override it through metadata.

The recent field is removed from compaction messages and the started/ended events. Old stored recent text remains readable through the compatibility decoder. keepID is the only name for the new reference—there is no alias for its unreleased earlier name.

5. Remove unused session.compacted

The unused transitional event is removed from the public event surface. Current compaction lifecycle events remain.

6. Provider compaction windows live in native.messages

 completed compaction / session.compaction.ended
-  native?           # summary call's step data, never read
-  providerContext?  { version, provenance, messages }
+  native?           { messages, ... }   # `messages` is the window replayed instead of `summary`

• A provider ("native") compaction replays its window only when the compaction's model has the current provider ID and model ID. That's the same rule assistant parts use. Otherwise history sends the original messages.
• Provenance (route, protocol, endpoint hash) and the request-hook route guards are removed. As a result:
  • a request hook that rewrites the base URL no longer blocks native compaction or replay;
  • the same model behind a changed endpoint still replays its window.
• Summary compactions no longer store the summary call's provider data in native. A compaction hook's result.native is still stored, and its native.messages is treated as a replay window.
• Old providerContext rows and events are converted to native.messages when read, including the media format from before 2.0.15.

Other visible changes

• Kept text from compactions saved before v2.1, and from V1 imports, is exposed as metadata.recent, which is where replay reads it. New compactions store only metadata.keepID.
• Versions before v2.1 can't load a session that has a compaction created by v2.1. Downgrades aren't supported.
• Older Effect SDK clients fail to decode compaction messages and events from a v2.1 server. Clients must match the server version.

Integration

Includes #56640, #56934, #56999, #56954, #57203, #57167, #57241 and #57286. Latest dev is merged into v2.1; the compaction conflict resolution retains both prompt-cache reuse and kept-message references. Generated client and OpenAPI files are updated.

The hosted-tool provider-switch fix remains separate in #57256. No release/version bump is included.

Verification

Run on v2.1 after #57241:

Additional verification for #57286: root checks, changed-file lint and generated-file checks pass. Live Anthropic server-side web search, web fetch and failed web fetch all replayed successfully after restarting the CLI. Stored data uses only tool.native; captured result blocks matched the stored payloads, including encrypted search content.