diff --git a/src/agents_shipgate/cli/scan/decision.py b/src/agents_shipgate/cli/scan/decision.py
index 3e828c3b..7917c91f 100644
--- a/src/agents_shipgate/cli/scan/decision.py
+++ b/src/agents_shipgate/cli/scan/decision.py
@@ -58,10 +58,12 @@ def _run_checks_and_decide(
     derived from sanitized tools. Mutating ``reason`` here would leak
     ``path:line`` into ``Finding.evidence``, churning fingerprints.
     """
+    action_surface_warnings: list[str] = []
     action_surface_facts = build_action_surface_facts(
         manifest,
         agent_id=tools_and_agent.agent.id,
         tools=tools_and_agent.tools,
+        warnings=action_surface_warnings,
     )
     capability_facts, capability_policy_subjects = build_capability_policy_subjects(
         manifest,
@@ -167,6 +169,7 @@ def _run_checks_and_decide(
     return _ChecksDecision(
         action_surface_facts=action_surface_facts,
         action_surface_diff=action_surface_diff,
+        action_surface_warnings=action_surface_warnings,
         findings=findings,
         legacy_fingerprints=legacy_fingerprints,
         override_resolution=override_resolution,
diff --git a/src/agents_shipgate/cli/scan/models.py b/src/agents_shipgate/cli/scan/models.py
index dc7bde2f..ecb314a0 100644
--- a/src/agents_shipgate/cli/scan/models.py
+++ b/src/agents_shipgate/cli/scan/models.py
@@ -103,6 +103,11 @@ class _ChecksDecision:
 
     action_surface_facts: ActionSurfaceFacts
     action_surface_diff: Any  # ActionSurfaceDiff (internal/semantic)
+    # Fail-soft warnings raised while building the action surface (e.g.
+    # duplicate action_id collisions from OpenAPI specs whose paths
+    # normalize identically). Merged into ``report.source_warnings`` so a
+    # third-party spec degrades to review_required instead of crashing.
+    action_surface_warnings: list[str]
     findings: list[Any]  # list[Finding]
     legacy_fingerprints: list[str]
     override_resolution: Any  # SeverityOverrideResolution
diff --git a/src/agents_shipgate/cli/scan/sanitization.py b/src/agents_shipgate/cli/scan/sanitization.py
index b4c9d737..ffb37a07 100644
--- a/src/agents_shipgate/cli/scan/sanitization.py
+++ b/src/agents_shipgate/cli/scan/sanitization.py
@@ -162,6 +162,17 @@ def _sanitize_for_output(
         stats=privacy_stats,
         path="source_warnings[]",
     )
+    # Fail-soft action-surface warnings (e.g. OpenAPI action_id collisions)
+    # are raised in Phase 5, after the Phase 3 source-warning list is
+    # assembled. Append them last so byte-stable output is preserved for
+    # the common (no-collision) case where this list is empty.
+    public_source_warnings.extend(
+        redact_data(
+            decision.action_surface_warnings,
+            stats=privacy_stats,
+            path="source_warnings[]",
+        )
+    )
     public_api_surface = redact_data(
         public_api_artifacts.surface_summary() if public_api_artifacts else None,
         stats=privacy_stats,
diff --git a/src/agents_shipgate/core/lenses/action_surface.py b/src/agents_shipgate/core/lenses/action_surface.py
index e43e8881..8195c5af 100644
--- a/src/agents_shipgate/core/lenses/action_surface.py
+++ b/src/agents_shipgate/core/lenses/action_surface.py
@@ -92,7 +92,23 @@ def build_action_surface_facts(
     *,
     agent_id: str,
     tools: list[Tool],
+    warnings: list[str] | None = None,
 ) -> ActionSurfaceFacts:
+    """Build the typed action surface from ``tools`` + manifest declarations.
+
+    Two distinct operations can derive the same ``action_id`` — most
+    commonly two OpenAPI operations whose paths normalize identically
+    (e.g. a trailing-slash variant of ``/sessions/{session_id}``), because
+    the OpenAPI ``operation`` token is ``METHOD path`` only and drops the
+    ``operationId``. A third-party spec must never crash a scan, so when a
+    ``warnings`` sink is provided the colliding ids are disambiguated
+    fail-soft and one ``source_warning`` is recorded per collision (same
+    fail-soft principle as the symlink-loop and MCP-as-tools fixes).
+
+    Callers that cannot tolerate a fail-soft snapshot (the redaction path,
+    which has its own public-only ordinal disambiguator) pass no sink and
+    keep the legacy hard :class:`ConfigError`.
+    """
     declarations = {entry.tool: entry for entry in manifest.action_surface.actions}
     actions = [
         _action_from_tool(
@@ -103,7 +119,26 @@ def build_action_surface_facts(
         )
         for tool in sorted(tools, key=lambda item: item.name)
     ]
-    _validate_unique_action_ids(actions)
+    if warnings is None:
+        _validate_unique_action_ids(actions)
+    else:
+        # Tools whose action_id carries a manifest-authored component. A
+        # collision touching one of these stays a hard ConfigError even on
+        # the fail-soft path — only inferred-vs-inferred collisions degrade.
+        # `id`, `provider`, and `operation` all override action_id
+        # components (see `build_action` / `_provider` / `_operation`), so a
+        # declaration setting any of them is an explicit identity the engine
+        # must never silently rewrite.
+        explicit_tool_names = {
+            entry.tool
+            for entry in manifest.action_surface.actions
+            if entry.id or entry.provider or entry.operation
+        }
+        warnings.extend(
+            _disambiguate_duplicate_action_ids(
+                actions, explicit_tool_names=explicit_tool_names
+            )
+        )
     return ActionSurfaceFacts(actions=sorted(actions, key=lambda item: item.action_id))
 
 
@@ -547,8 +582,11 @@ def _validate_unique_action_ids(actions: list[ActionFact]) -> None:
         for action_id, tool_names in by_id.items()
         if len(tool_names) > 1
     }
-    if not duplicates:
-        return
+    if duplicates:
+        _raise_duplicate_action_ids(duplicates)
+
+
+def _raise_duplicate_action_ids(duplicates: dict[str, list[str]]) -> None:
     details = "; ".join(
         f"{action_id!r} used by {', '.join(tool_names)}"
         for action_id, tool_names in sorted(duplicates.items())
@@ -560,6 +598,76 @@ def _validate_unique_action_ids(actions: list[ActionFact]) -> None:
     )
 
 
+def _disambiguate_duplicate_action_ids(
+    actions: list[ActionFact],
+    *,
+    explicit_tool_names: set[str],
+) -> list[str]:
+    """Fail-soft replacement for :func:`_validate_unique_action_ids`,
+    scoped to *inferred* collisions only.
+
+    A manifest-authored action identity — any ``action_surface.actions[]``
+    declaration setting ``id``, ``provider``, or ``operation`` — is a
+    contract: a collision that involves one (explicit-vs-explicit or
+    explicit-vs-inferred) is a config mistake to fix, so it stays a hard
+    :class:`ConfigError` (identical to the no-sink path).
+    ``explicit_tool_names`` names the tools carrying such a declaration.
+
+    Only collisions between purely *inferred* ids degrade — most commonly
+    two OpenAPI operations whose paths normalize identically. Those are
+    mutated in place so each ``action_id`` is unique, returning one
+    human-readable warning per resolved collision. The first member of each
+    colliding group (in ``tool_name`` order) keeps the bare id; the rest
+    gain a ``#<operationId>`` suffix so distinct operations stay distinct in
+    the diff. An ordinal fallback covers the pathological case where two
+    colliding actions also share a ``tool_name``. Renamed actions get a
+    refreshed ``identity_hash`` so downstream identity-hash consumers stay
+    consistent.
+    """
+    by_id: dict[str, list[ActionFact]] = {}
+    for action in actions:
+        by_id.setdefault(action.action_id, []).append(action)
+    colliding = {
+        action_id: group for action_id, group in by_id.items() if len(group) > 1
+    }
+
+    # Hard-fail any collision that touches an explicitly declared id. These
+    # are not third-party quirks the engine should silently rewrite.
+    explicit_collisions = {
+        action_id: sorted(item.tool_name for item in group)
+        for action_id, group in colliding.items()
+        if any(item.tool_name in explicit_tool_names for item in group)
+    }
+    if explicit_collisions:
+        _raise_duplicate_action_ids(explicit_collisions)
+
+    warnings: list[str] = []
+    for action_id, group in sorted(colliding.items()):
+        ordered = sorted(group, key=lambda item: item.tool_name)
+        warnings.append(
+            "Duplicate action_surface action_id "
+            f"{action_id!r} derived from operations "
+            f"{', '.join(repr(item.tool_name) for item in ordered)}; "
+            "disambiguated with per-operation suffixes so distinct "
+            "operations are not collapsed."
+        )
+        used_suffixes: dict[str, int] = {}
+        for index, action in enumerate(ordered):
+            if index == 0:
+                continue
+            suffix = action.tool_name or str(index)
+            seen = used_suffixes.get(suffix, 0) + 1
+            used_suffixes[suffix] = seen
+            if seen > 1:
+                suffix = f"{suffix}#{seen}"
+            new_id = f"{action_id}#{suffix}"
+            action.action_id = new_id
+            action.hashes = action.hashes.model_copy(
+                update={"identity_hash": _stable_hash(new_id)}
+            )
+    return warnings
+
+
 def _provider(tool: Tool, declaration: ActionDeclarationConfig | None) -> str:
     if declaration and declaration.provider:
         return _normalize_token(declaration.provider)
diff --git a/tests/test_action_surface_diff.py b/tests/test_action_surface_diff.py
index 77c69d3a..78029900 100644
--- a/tests/test_action_surface_diff.py
+++ b/tests/test_action_surface_diff.py
@@ -13,6 +13,7 @@
 from agents_shipgate.core.findings import assign_finding_ids
 from agents_shipgate.core.lenses.action_surface import (
     _dedupe_findings,
+    _stable_hash,
     build_action_surface_facts,
     compute_action_surface_diff,
     enrich_action_surface_diff_with_source,
@@ -209,6 +210,11 @@ def test_action_surface_rejects_duplicate_tool_declarations():
 
 
 def test_action_surface_rejects_action_id_collisions():
+    """An explicit ``actions[].id`` colliding with another action's inferred
+    id is a manifest config error and must stay a hard ConfigError — even on
+    the fail-soft (warnings-sink) path the live scan uses. Only purely
+    inferred collisions degrade; a user-declared id is never silently
+    rewritten."""
     manifest = _manifest(
         {
             "action_surface": {
@@ -244,6 +250,109 @@ def test_action_surface_rejects_action_id_collisions():
             agent_id="agent:action-test/agent",
             tools=tools,
         )
+    # The live scan path always passes a warnings sink; an explicit-vs-inferred
+    # collision must NOT be silently disambiguated into review_required.
+    with pytest.raises(ConfigError, match="Duplicate action_surface action_id"):
+        build_action_surface_facts(
+            manifest,
+            agent_id="agent:action-test/agent",
+            tools=tools,
+            warnings=[],
+        )
+
+
+def test_action_surface_rejects_collision_from_explicit_provider_operation():
+    """``provider``/``operation`` declarations override action_id components
+    just like ``id`` does. A collision between two such manifest-authored
+    identities must stay a hard ConfigError even on the warnings-sink path —
+    not be silently rewritten to ``...:shared#beta``."""
+    manifest = _manifest(
+        {
+            "action_surface": {
+                "actions": [
+                    {"tool": "alpha", "provider": "tools", "operation": "shared"},
+                    {"tool": "beta", "provider": "tools", "operation": "shared"},
+                ]
+            }
+        }
+    )
+    tools = [
+        Tool(
+            id="tool:alpha",
+            name="alpha",
+            source_type="mcp",
+            source_id="tools",
+            extraction_confidence="high",
+        ),
+        Tool(
+            id="tool:beta",
+            name="beta",
+            source_type="mcp",
+            source_id="tools",
+            extraction_confidence="high",
+        ),
+    ]
+
+    for sink in (None, []):
+        with pytest.raises(ConfigError, match="Duplicate action_surface action_id"):
+            build_action_surface_facts(
+                manifest,
+                agent_id="agent:action-test/agent",
+                tools=tools,
+                warnings=sink,
+            )
+
+
+def test_action_surface_disambiguates_openapi_action_id_collisions_fail_soft():
+    """Two OpenAPI operations whose paths normalize identically (a
+    trailing-slash variant) collapse to one ``action_id``. With a warnings
+    sink the scan degrades instead of raising: ids stay distinct and one
+    warning is recorded. Real-world repro: block/goose's spec."""
+    manifest = _manifest()
+    tools = [
+        Tool(
+            id="tool:get_session",
+            name="get_session",
+            source_type="openapi",
+            source_id="goose-api",
+            annotations={"httpMethod": "get", "path": "/sessions/{session_id}"},
+            extraction_confidence="high",
+        ),
+        Tool(
+            id="tool:get_session_detail",
+            name="get_session_detail",
+            source_type="openapi",
+            source_id="goose-api",
+            # Trailing slash normalizes to the same path as get_session.
+            annotations={"httpMethod": "get", "path": "/sessions/{session_id}/"},
+            extraction_confidence="high",
+        ),
+    ]
+
+    warnings: list[str] = []
+    facts = build_action_surface_facts(
+        manifest,
+        agent_id="agent:action-test/agent",
+        tools=tools,
+        warnings=warnings,
+    )
+
+    action_ids = [action.action_id for action in facts.actions]
+    base_id = "agent:action-test/agent:openapi:goose-api:GET /sessions/{session_id}"
+    # Both operations are retained as distinct actions; the first (in
+    # tool-name order) keeps the bare id, the second is suffixed.
+    assert action_ids == sorted([base_id, f"{base_id}#get_session_detail"])
+    assert len(set(action_ids)) == 2
+    assert {action.tool_name for action in facts.actions} == {
+        "get_session",
+        "get_session_detail",
+    }
+    # identity_hash tracks the renamed action_id.
+    suffixed = next(a for a in facts.actions if a.action_id.endswith("#get_session_detail"))
+    assert suffixed.hashes.identity_hash == _stable_hash(suffixed.action_id)
+    assert len(warnings) == 1
+    assert "Duplicate action_surface action_id" in warnings[0]
+    assert "get_session" in warnings[0] and "get_session_detail" in warnings[0]
 
 
 def test_action_surface_policy_requires_typed_expected_values():
diff --git a/tests/test_scan.py b/tests/test_scan.py
index 15861f87..e7e058cd 100644
--- a/tests/test_scan.py
+++ b/tests/test_scan.py
@@ -1327,3 +1327,97 @@ def test_scan_writes_no_suggested_inventory_when_confidence_is_high(tmp_path):
         packet_enabled=False,
     )
     assert not (tmp_path / "suggested-inventory.json").exists()
+
+
+def test_openapi_action_id_collision_degrades_instead_of_crashing(tmp_path):
+    """A valid third-party OpenAPI spec with two operations that normalize
+    to the same ``method + path`` must never crash a scan with a hard
+    Config error. Regression for the block/goose miner finding: two GET
+    operations on ``/sessions/{session_id}`` (one a trailing-slash variant)
+    collapsed to one ``action_id`` and hard-failed the duplicate-id guard.
+    Same fail-soft principle as the symlink-loop (#212) and MCP-as-tools
+    (#214) fixes: degrade to a source_warning, keep both operations.
+    """
+    project = tmp_path / "project"
+    project.mkdir()
+    # Two GET operations whose paths normalize identically (the second has
+    # a trailing slash), each with a distinct operationId — exactly the
+    # shape goose's spec ships.
+    (project / "openapi.yaml").write_text(
+        """
+openapi: 3.1.0
+info:
+  title: Goose-like API
+  version: "1.0"
+paths:
+  /sessions/{session_id}:
+    get:
+      operationId: get_session
+      summary: Get a session.
+      parameters:
+        - name: session_id
+          in: path
+          required: true
+          schema: {type: string}
+      responses:
+        "200":
+          description: ok
+  /sessions/{session_id}/:
+    get:
+      operationId: get_session_detail
+      summary: Get a session detail.
+      parameters:
+        - name: session_id
+          in: path
+          required: true
+          schema: {type: string}
+      responses:
+        "200":
+          description: ok
+""",
+        encoding="utf-8",
+    )
+    (project / "shipgate.yaml").write_text(
+        """
+version: "0.1"
+project:
+  name: goose-collision
+agent:
+  name: goose-agent
+  declared_purpose:
+    - test action_id collision degradation
+environment:
+  target: local
+tool_sources:
+  - id: goose-api
+    type: openapi
+    path: openapi.yaml
+""",
+        encoding="utf-8",
+    )
+
+    # Must not raise ConfigError — the scan completes and returns a report.
+    report, exit_code = run_scan(
+        config_path=project / "shipgate.yaml",
+        output_dir=tmp_path / "reports",
+        formats=["json"],
+        ci_mode="advisory",
+        packet_enabled=False,
+    )
+
+    # advisory mode never fails the build; in particular it is not the
+    # config-error exit code.
+    assert exit_code == 0
+    # Both operations survive as distinct actions (one disambiguated).
+    action_ids = {action.action_id for action in report.action_surface_facts.actions}
+    assert len(action_ids) == 2
+    assert {a.tool_name for a in report.action_surface_facts.actions} == {
+        "get_session",
+        "get_session_detail",
+    }
+    # The collision is surfaced as a source_warning (routes to
+    # review_required), not swallowed.
+    assert any(
+        "Duplicate action_surface action_id" in warning
+        for warning in report.source_warnings
+    ), f"Expected an action_id collision warning; got: {report.source_warnings}"