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/subplan_execution_coverage_boost.feature

@@ -0,0 +1,55 @@
+@subplan @coverage_boost
+Feature: Subplan Execution Service – Defensive Code Path Coverage
+  As a developer maintaining the subplan execution service
+  I want to exercise the defensive error-handling code paths
+  So that coverage includes the safety-net branches for parallel, wave, and dependency-ordered execution
+
+  # --- Parallel execution: generic Exception from future.result() (lines 298-303) ---
+
+  @parallel @defensive
+  Scenario: Parallel execution catches generic exception from future and marks subplan ERRORED
+    Given a subplan execution service in parallel mode with 2 subplans
+    And the internal retry method is patched to raise a RuntimeError for the first subplan
+    When parallel execution is invoked
+    Then the first subplan should be marked ERRORED with the RuntimeError message
+    And the second subplan should complete normally
+
+  # --- Parallel execution: safety-net for uncaptured futures (lines 331-334) ---
+
+  @parallel @defensive
+  Scenario: Parallel fail-fast safety net cancels subplans missing from as_completed results
+    Given a subplan execution service in parallel fail-fast mode with 3 subplans
+    And as_completed is patched to skip the third future and the first subplan fails
+    When parallel execution is invoked with patched as_completed
+    Then the third subplan should be marked CANCELLED by the safety net
+    And the results should contain all 3 subplans
+
+  # --- Dependency-ordered: empty ready list causes break (line 381) ---
+
+  @dependency_ordered @defensive
+  Scenario: Dependency-ordered execution breaks out when no nodes are ready due to unresolvable deps
+    Given a subplan execution service in dependency-ordered mode with 2 subplans
+    And topological sort is patched to accept a circular dependency graph
+    When dependency-ordered execution is invoked with the circular graph
+    Then execution should complete without raising an error
+    And the number of completed subplans should be less than 2
+
+  # --- Wave execution: CancelledError from future.result() (lines 573-575) ---
+
+  @wave @defensive
+  Scenario: Wave execution catches CancelledError from a future and marks subplan CANCELLED
+    Given a subplan execution service in dependency-ordered mode with 3 independent subplans
+    And the internal retry method is patched to raise CancelledError for the second subplan in wave
+    When dependency-ordered execution is invoked for the wave scenario
+    Then the second subplan should be marked CANCELLED
+    And the other subplans in the wave should complete successfully
+
+  # --- Wave execution: generic Exception from future.result() (lines 576-578) ---
+
+  @wave @defensive
+  Scenario: Wave execution catches generic Exception from a future and marks subplan ERRORED
+    Given a subplan execution service in dependency-ordered mode with 3 independent subplans for exception test
+    And the internal retry method is patched to raise ValueError for the second subplan in wave
+    When dependency-ordered execution is invoked for the wave exception scenario
+    Then the second subplan should be marked ERRORED with the ValueError message
+    And the other wave subplans should still complete