test(coverage): add Behave BDD tests to improve unit test coverage across 53 source modules

Add 53 new .feature files and corresponding step definition files targeting
uncovered lines identified in build/coverage.xml. Fix AmbiguousStep conflicts
in 7 pre-existing step files by disambiguating step text.

New tests cover: ACP clients/facade, actor CLI/config, application container,
ACMS service/strategies, async worker, automation profile CLI, autonomy
guardrail, bridge, change model, config CLI/service, context service,
cross-plan correction, database models, decision service, decomposition
clustering/service, discovery handler, langchain chat provider, langgraph
nodes, materializers, multi-project service, plan apply/CLI/lifecycle/model/
preflight/resume/service, PostgreSQL analyzer, project CLI/context CLI,
provider registry, reactive application/route, repositories, resolver handler,
resource registry service, resume model, retry patterns, sandbox protocol,
server CLI, skill CLI/service, skills registry, subplan execution/service,
system CLI, UKO loader, UoW, and YAML template engine.

Closes #645

features/sandbox_protocol_coverage_boost.feature

@@ -0,0 +1,98 @@
+Feature: Sandbox protocol coverage boost
+  Exercise uncovered lines in infrastructure/sandbox/protocol.py including
+  SandboxStatus.assert_transition error path and Sandbox Protocol default stubs.
+
+  # ---------------------------------------------------------------
+  # SandboxStatus.assert_transition – invalid transition raises error
+  # Covers lines 121-123
+  # ---------------------------------------------------------------
+
+  Scenario: assert_transition raises SandboxStateError for invalid transition
+    Given spcb sandbox status "cleaned_up" and target status "active"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "cleaned_up -> active"
+
+  Scenario: assert_transition raises SandboxStateError for pending to committed
+    Given spcb sandbox status "pending" and target status "committed"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "pending -> committed"
+
+  Scenario: assert_transition raises SandboxStateError for committed to active
+    Given spcb sandbox status "committed" and target status "active"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "committed -> active"
+
+  Scenario: assert_transition succeeds for valid pending to created transition
+    Given spcb sandbox status "pending" and target status "created"
+    When spcb assert_transition is called with those statuses
+    Then spcb no exception should be raised
+
+  # ---------------------------------------------------------------
+  # Sandbox Protocol default property/method stubs
+  # Covers lines 223, 228, 233, 248, 263, 278, 290, 301
+  # ---------------------------------------------------------------
+
+  Scenario: Protocol sandbox_id default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the sandbox_id property is accessed
+    Then spcb the result should be None
+
+  Scenario: Protocol status default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the status property is accessed
+    Then spcb the result should be None
+
+  Scenario: Protocol context default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the context property is accessed
+    Then spcb the result should be None
+
+  Scenario: Protocol create default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the create method is called with plan_id "test-plan"
+    Then spcb the result should be None
+
+  Scenario: Protocol get_path default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the get_path method is called with path "src/main.py"
+    Then spcb the result should be None
+
+  Scenario: Protocol commit default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the commit method is called with message "test commit"
+    Then spcb the result should be None
+
+  Scenario: Protocol rollback default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the rollback method is called
+    Then spcb the result should be None
+
+  Scenario: Protocol cleanup default stub returns None
+    Given spcb a bare Sandbox protocol subclass instance
+    When spcb the cleanup method is called
+    Then spcb the result should be None
+
+  # ---------------------------------------------------------------
+  # Additional assert_transition edge cases for branch coverage
+  # ---------------------------------------------------------------
+
+  Scenario: assert_transition raises for every terminal-state outbound attempt
+    Given spcb sandbox status "cleaned_up" and target status "pending"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "cleaned_up -> pending"
+
+  Scenario: assert_transition raises for errored to active
+    Given spcb sandbox status "errored" and target status "active"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "errored -> active"
+
+  Scenario: assert_transition raises for rolled_back to committed
+    Given spcb sandbox status "rolled_back" and target status "committed"
+    When spcb assert_transition is called with those statuses
+    Then spcb a SandboxStateError should be raised
+    And spcb the error message should contain "rolled_back -> committed"