tests/interaction: tag arm_exclusions per-requirement, not minimal-covering-set

The earlier annotation passes minimised by tagging only one requirement
ID per multi-decorated test, relying on compute_cells() intersection to
drop the cell. That left the manifest's per-requirement semantics
incomplete: the ArmExclusionReason enum is documented as a re-admission
checklist (grep the reason to find what to re-admit), which only works
if every semantically-excluded requirement carries the exclusion.

15 entries now carry their own arm_exclusions instead of inheriting via
a sibling on the same test:

- 12 server-initiated-request / requires-session entries gain both the
  streamable-http-stateless and spec_version=2026-07-28 exclusions
  (sampling:create:model-preferences/system-prompt, elicitation:form:
  basic/action:accept/schema:enum-variants, etc.)
- 3 capability:declared entries (resources/prompts/completion) gain the
  legacy-only-vocabulary 2026 exclusion, matching tools:capability:declared

lifecycle:initialize:capabilities:from-handlers and mcpserver:context:
logging are deliberately not tagged (open classification question /
era-agnostic respectively).

Also: the README transport-matrix section now mentions all four
connectable transports and the stateless carve-out, matching the
era-axis section.

504 connect cells unchanged; 53 stateless / 56 2026 arm_exclusions;
100% coverage.

Author: maxisbey

tests/interaction/README.md

@@ -56,10 +56,12 @@ test body — each directory pins its flavour's true output exactly.
 
 Transport-agnostic tests take the `connect` fixture instead of constructing `Client(server)`
 directly, and therefore run once per transport: over the in-memory transport, over the server's
-real streamable HTTP app driven in-process through the streaming bridge, and over the legacy SSE
-transport the same way. A test connects with `async with connect(server, ...) as client:` and
-asserts the same output on every leg, because the transport is not supposed to change observable
-behaviour. Tests that are tied to one transport do not use the fixture: the wire-recording tests
+real streamable HTTP app driven in-process through the streaming bridge (in both stateful and
+stateless configurations), and over the legacy SSE transport the same way. A test connects with
+`async with connect(server, ...) as client:` and asserts the same output on every leg, because the
+transport is not supposed to change observable behaviour. Requirements that need a server-to-client
+back-channel or persisted session state are carved out of the stateless arm via `arm_exclusions`.
+Tests that are tied to one transport do not use the fixture: the wire-recording tests
 (their seam is the in-memory stream pair), the bare-`ClientSession` lifecycle tests, the
 real-clock timeout tests (the timeout machinery is transport-independent and must not race
 transport latency), and everything under `transports/`, which pins behaviour only observable on

tests/interaction/_requirements.py

@@ -351,6 +351,10 @@ def __post_init__(self) -> None:
     "protocol:cancel:handler-abort-propagates": Requirement(
         source=f"{SPEC_BASE_URL}/basic/utilities/cancellation#behavior-requirements",
         behavior="On the receiving side, a cancellation notification stops the running request handler.",
+        arm_exclusions=(
+            ArmExclusion(reason="requires-session", transport="streamable-http-stateless"),
+            ArmExclusion(reason="requires-session", spec_version="2026-07-28"),
+        ),
     ),
     "protocol:cancel:in-flight": Requirement(
         source=f"{SPEC_BASE_URL}/basic/utilities/cancellation#behavior-requirements",
@@ -535,6 +539,10 @@ def __post_init__(self) -> None:
             "A progress notification that arrives after its request has completed is not delivered to the "
             "original progress callback."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="requires-session", transport="streamable-http-stateless"),
+            ArmExclusion(reason="requires-session", spec_version="2026-07-28"),
+        ),
     ),
     "protocol:progress:no-token": Requirement(
         source=f"{SPEC_BASE_URL}/basic/utilities/progress#progress-flow",
@@ -660,6 +668,10 @@ def __post_init__(self) -> None:
             "A tool handler that issues a sampling request receives the client's completion and can embed "
             "it in the tool call result."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "tools:call:structured-content": Requirement(
         source=f"{SPEC_BASE_URL}/server/tools#structured-content",
@@ -882,6 +894,10 @@ def __post_init__(self) -> None:
             "Context.elicit sends a form elicitation built from a typed schema and returns a typed "
             "accepted/declined/cancelled result."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "mcpserver:context:read-resource": Requirement(
         source="sdk",
@@ -906,6 +922,7 @@ def __post_init__(self) -> None:
             "A server with resource handlers advertises the resources capability, including the subscribe "
             "sub-flag when a subscribe handler is registered."
         ),
+        arm_exclusions=(ArmExclusion(reason="legacy-only-vocabulary", spec_version="2026-07-28"),),
     ),
     "resources:list-changed": Requirement(
         source=f"{SPEC_BASE_URL}/server/resources#list-changed-notification",
@@ -1062,6 +1079,7 @@ def __post_init__(self) -> None:
     "prompts:capability:declared": Requirement(
         source=f"{SPEC_BASE_URL}/server/prompts#capabilities",
         behavior="A server with a list_prompts handler advertises the prompts capability in its initialize result.",
+        arm_exclusions=(ArmExclusion(reason="legacy-only-vocabulary", spec_version="2026-07-28"),),
     ),
     "prompts:get:content:audio": Requirement(
         source=f"{SPEC_BASE_URL}/server/prompts#audio-content",
@@ -1164,6 +1182,7 @@ def __post_init__(self) -> None:
     "completion:capability:declared": Requirement(
         source=f"{SPEC_BASE_URL}/server/utilities/completion#capabilities",
         behavior="A server with a completion handler advertises the completions capability in its initialize result.",
+        arm_exclusions=(ArmExclusion(reason="legacy-only-vocabulary", spec_version="2026-07-28"),),
     ),
     "completion:complete:not-supported": Requirement(
         source=f"{SPEC_BASE_URL}/server/utilities/completion#capabilities",
@@ -1308,17 +1327,29 @@ def __post_init__(self) -> None:
                 "capability; the server-side validator only checks tools/tool_choice."
             ),
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "sampling:create:model-preferences": Requirement(
         source=f"{SPEC_BASE_URL}/client/sampling#model-preferences",
         behavior=(
             "The model preferences supplied by the server (hints and the cost, speed, and intelligence "
             "priorities) reach the client callback intact."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "sampling:create:system-prompt": Requirement(
         source=f"{SPEC_BASE_URL}/client/sampling#creating-messages",
         behavior="The system prompt supplied by the server reaches the client callback intact.",
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "sampling:create:tools": Requirement(
         source=f"{SPEC_BASE_URL}/client/sampling#tools-in-sampling",
@@ -1494,13 +1525,21 @@ def __post_init__(self) -> None:
                 "elicitation/create; the spec's MUST NOT is not enforced."
             ),
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "elicitation:form:action:accept": Requirement(
         source=f"{SPEC_BASE_URL}/client/elicitation#response-actions",
         behavior=(
             "A form-mode elicitation answered with action 'accept' returns the user's content to the "
             "requesting handler."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "elicitation:form:action:cancel": Requirement(
         source=f"{SPEC_BASE_URL}/client/elicitation#response-actions",
@@ -1524,6 +1563,10 @@ def __post_init__(self) -> None:
             "A form-mode elicitation delivers the message and requested schema to the client callback "
             "exactly as the server sent them."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "elicitation:form:defaults": Requirement(
         source=f"{SPEC_BASE_URL}/client/elicitation#requested-schema",
@@ -1560,6 +1603,10 @@ def __post_init__(self) -> None:
             "Requested-schema enum fields (including titled and multi-select variants) reach the client "
             "callback as sent."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "elicitation:form:schema:primitives": Requirement(
         source=f"{SPEC_BASE_URL}/client/elicitation#requested-schema",
@@ -1615,6 +1662,10 @@ def __post_init__(self) -> None:
             "response carries no content (accept means the user agreed to visit the URL, not that the "
             "interaction completed)."
         ),
+        arm_exclusions=(
+            ArmExclusion(reason="server-initiated-request", transport="streamable-http-stateless"),
+            ArmExclusion(reason="server-initiated-request", spec_version="2026-07-28"),
+        ),
     ),
     "elicitation:url:basic": Requirement(
         source=f"{SPEC_BASE_URL}/client/elicitation#url-mode-elicitation-requests",