diff --git a/docs/extension-specifications.md b/docs/extension-specifications.md
index 5e5589c..1100ced 100644
--- a/docs/extension-specifications.md
+++ b/docs/extension-specifications.md
@@ -69,8 +69,15 @@ Extension URI: `urn:opencode-a2a:extension:shared:stream-hints:v1`
 - Scope: shared response/task/stream metadata for block identity, progress, and usage hints
 - Disclosure: public Agent Card and authenticated extended Agent Card
 - Activation: client requests the URI via `A2A-Extensions`; runtime emits shared metadata on streamed events and final task payloads
-- Runtime fields: `metadata.shared.stream`, `metadata.shared.progress`, `metadata.shared.usage`
-- Detailed-only correlation fields: `metadata.shared.stream.message_id` and `metadata.shared.stream.event_id` may be emitted for timeline stitching and diagnostics, but are not part of the minimum public consumer contract
+- Declared field map:
+  - `metadata.shared.stream.block_type`
+  - `metadata.shared.stream.sequence`
+  - `metadata.shared.progress.type`
+  - `metadata.shared.progress.status`
+  - `metadata.shared.usage.input_tokens`
+  - `metadata.shared.usage.output_tokens`
+  - `metadata.shared.usage.total_tokens`
+- Clients must not treat undeclared metadata under this namespace as part of the shared v1 contract
 - Dependencies: none declared by this version
 - Security boundary: this extension is observational metadata only; callback methods are defined by the separate shared interactive interrupt extension
 - Versioning: breaking changes require a new versioned URI
diff --git a/docs/guide.md b/docs/guide.md
index 28b0483..cd17576 100644
--- a/docs/guide.md
+++ b/docs/guide.md
@@ -229,9 +229,7 @@ If one deployment works while another fails against the same upstream provider,
   - text chunks use a stable text artifact ID
   - reasoning chunks use a stable reasoning artifact ID
   - tool-call updates use a stable per-tool-part artifact ID when the upstream part is identifiable
-- `artifact.metadata.shared.stream.event_id` preserves the original cross-artifact stream timeline, even when different logical lanes use different artifact IDs.
-- `artifact.metadata.shared.stream.message_id` remains best-effort metadata: when upstream omits `message_id`, the service falls back to a stable request-scoped message identity.
-- `message_id` and `event_id` are advanced correlation fields: they help timeline stitching, deduplication, diagnostics, and advanced UI linking, but generic A2A consumers must not require them.
+- The shared stream-hints v1 contract only declares `block_type` and `sequence` under `artifact.metadata.shared.stream`.
 - `artifact.metadata.shared.stream.sequence` carries the canonical per-request stream sequence.
 - A final complete text snapshot is emitted only when streaming chunks did not already produce the same final text.
 - That final complete text snapshot uses `append=false` on the text artifact so clients and the task store can treat it as the canonical replace-on-finish version rather than another fragment.
@@ -242,7 +240,7 @@ If one deployment works while another fails against the same upstream provider,
 - If `application/json` is not accepted but `text/plain` is still accepted, those `tool_call` blocks are downgraded to stable compact JSON text so text-only clients retain the same observable state transitions.
 - When a request restricts `acceptedOutputModes`, the stream applies the same output filtering before persistence so later task snapshots do not re-expose filtered structured blocks.
 - Persistence is canonicalized separately from transport: stream subscribers still receive incremental artifact updates, while task-store persistence rewrites those updates into compact per-artifact snapshots so `GetTask` and terminal replay do not accumulate token-level fragments.
-- Final status event metadata may include normalized token usage at `metadata.shared.usage` with fields such as `input_tokens`, `output_tokens`, `total_tokens`, optional `reasoning_tokens`, optional `cache_tokens.read_tokens` / `cache_tokens.write_tokens`, and optional `cost`.
+- The shared stream-hints v1 contract declares normalized usage fields `input_tokens`, `output_tokens`, and `total_tokens` at `metadata.shared.usage`.
 - Progress metadata at `metadata.shared.progress` is emitted only when the client negotiated `urn:opencode-a2a:extension:shared:stream-hints:v1`; baseline streams do not emit duplicate generic `working` status updates just to carry progress hints.
 - Usage is extracted from documented info payloads and supported usage parts such as `step-finish`; non-usage parts with similar fields are ignored.
 - Interrupt events (`permission.asked` / `question.asked`) are mapped to `TaskStatusUpdateEvent(final=false, state=input-required)` with details at `metadata.shared.interrupt` when the client negotiated `urn:opencode-a2a:extension:shared:interactive-interrupt:v1`.
@@ -572,24 +570,25 @@ Runtime payload:
 Shared runtime fields:
 
 - `metadata.shared.stream`
-  - block-level stream metadata such as `block_type`, `message_id`, `event_id`, and `sequence`
+  - declared shared v1 fields: `block_type` and `sequence`
 - `metadata.shared.usage`
-  - normalized usage data such as `input_tokens`, `output_tokens`, `total_tokens`, optional `reasoning_tokens`, optional `cache_tokens.read_tokens` / `cache_tokens.write_tokens`, and optional `cost`
+  - declared shared v1 fields: `input_tokens`, `output_tokens`, and `total_tokens`
+- clients must ignore undeclared fields when interpreting the shared v1 contract
 
 Consumer guidance:
 
 - Use the extension declaration to know the server emits canonical shared stream hints.
 - Use runtime metadata to render block timelines, progress states, and token usage.
-- Treat `message_id` and `event_id` as optional advanced correlation fields rather than baseline consumer requirements.
+- Do not rely on undeclared fields under `metadata.shared.stream` or `metadata.shared.usage` as stable contract surface.
 - Do not infer capability support only from seeing one runtime field on one response; rely on Agent Card discovery first when possible.
 
 Minimal stream semantics summary:
 
 - `text`, `reasoning`, and `tool_call` are emitted as canonical block types
 - `text` and `reasoning` blocks use text parts, while `tool_call` uses structured v1 part payloads
-- `message_id` and `event_id` preserve stable timeline identity where possible and are emitted only as optional advanced correlation hints
+- only `block_type` and `sequence` are part of the declared shared stream field map
 - `sequence` is the per-request canonical stream sequence
-- final task/status metadata may repeat normalized usage after the streaming phase ends
+- final task/status metadata may repeat declared usage totals
 
 ## OpenCode Session Management A2A Extension
 
diff --git a/src/opencode_a2a/contracts/extensions/public_params.py b/src/opencode_a2a/contracts/extensions/public_params.py
index e0cf26f..633e98a 100644
--- a/src/opencode_a2a/contracts/extensions/public_params.py
+++ b/src/opencode_a2a/contracts/extensions/public_params.py
@@ -53,26 +53,42 @@ def select_public_extension_params(
     return {key: params[key] for key in keys if key in params}
 
 
+_DECLARED_SHARED_STREAM_FIELD_KEYS = ("block_type", "sequence")
+_DECLARED_SHARED_PROGRESS_FIELD_KEYS = ("type", "status")
+_DECLARED_SHARED_USAGE_FIELD_KEYS = ("input_tokens", "output_tokens", "total_tokens")
+
+
+def _build_declared_streaming_metadata_fields(
+    params: dict[str, Any],
+) -> tuple[dict[str, Any], dict[str, Any], dict[str, Any]]:
+    return (
+        select_public_extension_params(
+            params["stream_fields"],
+            keys=_DECLARED_SHARED_STREAM_FIELD_KEYS,
+        ),
+        select_public_extension_params(
+            params["progress_fields"],
+            keys=_DECLARED_SHARED_PROGRESS_FIELD_KEYS,
+        ),
+        select_public_extension_params(
+            params["usage_fields"],
+            keys=_DECLARED_SHARED_USAGE_FIELD_KEYS,
+        ),
+    )
+
+
 def build_public_streaming_extension_params(
     params: dict[str, Any],
 ) -> dict[str, Any]:
+    stream_fields, progress_fields, usage_fields = _build_declared_streaming_metadata_fields(params)
     return {
         "artifact_metadata_field": params["artifact_metadata_field"],
         "progress_metadata_field": params["progress_metadata_field"],
         "usage_metadata_field": params["usage_metadata_field"],
         "block_types": params["block_types"],
-        "stream_fields": select_public_extension_params(
-            params["stream_fields"],
-            keys=("block_type", "sequence"),
-        ),
-        "progress_fields": select_public_extension_params(
-            params["progress_fields"],
-            keys=("type", "status"),
-        ),
-        "usage_fields": select_public_extension_params(
-            params["usage_fields"],
-            keys=("input_tokens", "output_tokens", "total_tokens"),
-        ),
+        "stream_fields": stream_fields,
+        "progress_fields": progress_fields,
+        "usage_fields": usage_fields,
     }
 
 
@@ -177,6 +193,28 @@ def build_model_selection_extension_params(
 
 
 def build_streaming_extension_params() -> dict[str, Any]:
+    stream_fields = {
+        "block_type": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.block_type",
+        "sequence": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.sequence",
+    }
+    progress_fields = {
+        "type": f"{identifiers.SHARED_PROGRESS_METADATA_FIELD}.type",
+        "status": f"{identifiers.SHARED_PROGRESS_METADATA_FIELD}.status",
+    }
+    usage_fields = {
+        "input_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.input_tokens",
+        "output_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.output_tokens",
+        "total_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.total_tokens",
+    }
+    declared_stream_fields, declared_progress_fields, declared_usage_fields = (
+        _build_declared_streaming_metadata_fields(
+            {
+                "stream_fields": stream_fields,
+                "progress_fields": progress_fields,
+                "usage_fields": usage_fields,
+            }
+        )
+    )
     return {
         "artifact_metadata_field": identifiers.SHARED_STREAM_METADATA_FIELD,
         "status_metadata_field": identifiers.SHARED_STREAM_METADATA_FIELD,
@@ -207,31 +245,9 @@ def build_streaming_extension_params() -> dict[str, Any]:
                 },
             },
         },
-        "stream_fields": {
-            "block_type": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.block_type",
-            "message_id": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.message_id",
-            "event_id": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.event_id",
-            "sequence": f"{identifiers.SHARED_STREAM_METADATA_FIELD}.sequence",
-        },
-        "progress_fields": {
-            "type": f"{identifiers.SHARED_PROGRESS_METADATA_FIELD}.type",
-            "status": f"{identifiers.SHARED_PROGRESS_METADATA_FIELD}.status",
-        },
-        "usage_fields": {
-            "input_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.input_tokens",
-            "output_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.output_tokens",
-            "total_tokens": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.total_tokens",
-            "reasoning_tokens": (f"{identifiers.SHARED_USAGE_METADATA_FIELD}.reasoning_tokens"),
-            "cost": f"{identifiers.SHARED_USAGE_METADATA_FIELD}.cost",
-            "cache_tokens": {
-                "read_tokens": (
-                    f"{identifiers.SHARED_USAGE_METADATA_FIELD}.cache_tokens.read_tokens"
-                ),
-                "write_tokens": (
-                    f"{identifiers.SHARED_USAGE_METADATA_FIELD}.cache_tokens.write_tokens"
-                ),
-            },
-        },
+        "stream_fields": declared_stream_fields,
+        "progress_fields": declared_progress_fields,
+        "usage_fields": declared_usage_fields,
     }
 
 
diff --git a/tests/server/test_agent_card.py b/tests/server/test_agent_card.py
index 4c858f2..e16275f 100644
--- a/tests/server/test_agent_card.py
+++ b/tests/server/test_agent_card.py
@@ -172,6 +172,14 @@ def test_public_agent_card_is_slimmed_but_keeps_core_shared_contract_hints() ->
             "phase": "metadata.shared.interrupt.phase",
         },
     }
+    assert (
+        extended_ext_by_uri[STREAMING_EXTENSION_URI].params["stream_fields"]
+        == ext_by_uri[STREAMING_EXTENSION_URI].params["stream_fields"]
+    )
+    assert (
+        extended_ext_by_uri[STREAMING_EXTENSION_URI].params["usage_fields"]
+        == ext_by_uri[STREAMING_EXTENSION_URI].params["usage_fields"]
+    )
 
     for uri in AUTHENTICATED_ONLY_EXTENSION_URIS:
         assert uri not in ext_by_uri
@@ -320,12 +328,6 @@ def test_agent_card_injects_profile_into_extensions() -> None:
         "input_tokens": "metadata.shared.usage.input_tokens",
         "output_tokens": "metadata.shared.usage.output_tokens",
         "total_tokens": "metadata.shared.usage.total_tokens",
-        "reasoning_tokens": "metadata.shared.usage.reasoning_tokens",
-        "cost": "metadata.shared.usage.cost",
-        "cache_tokens": {
-            "read_tokens": "metadata.shared.usage.cache_tokens.read_tokens",
-            "write_tokens": "metadata.shared.usage.cache_tokens.write_tokens",
-        },
     }
 
     session_management = ext_by_uri[SESSION_MANAGEMENT_EXTENSION_URI]