From d0248b474b26c871bf17712d641b58f5673d07bc Mon Sep 17 00:00:00 2001
From: Yernat Yestekov <2068106+doublewhy@users.noreply.github.com>
Date: Wed, 12 Aug 2026 12:34:15 -0700
Subject: [PATCH] test(runtime): bind wall readback to predecessor (#1122)

---
 ...-437-wall-readback-concurrency-addendum.md | 40 +++++++++++++++++++
 docs/requirements/DSL-437/requirement.md      |  5 ++-
 ...st_dsl_437_benign_participant_execution.py |  4 +-
 3 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 docs/decisions/issue-1122-dsl-437-wall-readback-concurrency-addendum.md

diff --git a/docs/decisions/issue-1122-dsl-437-wall-readback-concurrency-addendum.md b/docs/decisions/issue-1122-dsl-437-wall-readback-concurrency-addendum.md
new file mode 100644
index 00000000..4958c5e9
--- /dev/null
+++ b/docs/decisions/issue-1122-dsl-437-wall-readback-concurrency-addendum.md
@@ -0,0 +1,40 @@
+# Issue 1122 Wall-Readback Concurrency Addendum
+
+Date: 2026-08-12
+
+Issue: #1122. Requirement: DSL-437. Related: #861.
+
+## Gap And Existing Surface
+
+The DSL-437 wall-driver regression assumed that a real-time clock remained at
+absolute tick zero after `RuntimeManager.apply()` started its driver. Under
+contention, the driver may validly advance before a reader acquires the shared
+participant-execution lock. The incumbent lock, time-runtime readback, snapshot,
+and wall-driver surfaces are sufficient; this is a test-oracle defect, not a
+new runtime semantic or public contract.
+
+## Decision
+
+A blocked-read concurrency check binds its result to the full predecessor
+`TimeCoordinateModel` captured for that critical section. The test holds the
+runtime read inside the shared lock, captures the predecessor snapshot, waits
+longer than one wall tick, and proves that the manager snapshot remains
+unchanged. After release, the returned segment, tick, and microstep must equal
+the captured predecessor coordinate.
+
+This evidence does not assert absolute tick zero. A valid wall advance before
+the blocked read is outside the critical section being tested and cannot make
+the result fail. An advance during the read still changes the snapshot or
+returned coordinate and fails deterministically.
+
+## Alternatives And Verification
+
+Retaining `tick == 0` was rejected because scheduler contention can invalidate
+that unrelated timing assumption. Sleeping less or increasing the tick period
+only changes the race probability. Injecting a private test clock was rejected
+because the existing predecessor snapshot is the canonical shared-time state
+cut and no runtime hook is required.
+
+Verification runs the focused blocked-read test repeatedly under CPython 3.14
+free-threaded contention, the surrounding DSL-437 wall-driver tests, Ruff, and
+the DSL-437 requirement and repository policy gates.
diff --git a/docs/requirements/DSL-437/requirement.md b/docs/requirements/DSL-437/requirement.md
index aa4821f1..478b9f7a 100644
--- a/docs/requirements/DSL-437/requirement.md
+++ b/docs/requirements/DSL-437/requirement.md
@@ -6,7 +6,7 @@ type: FUNCTIONAL
 priority: MUST
 wave: 1
 created_at: 2026-07-24T04:32:00.397864Z
-updated_at: 2026-07-24T14:02:11.974014Z
+updated_at: 2026-08-12T00:00:00.000000Z
 ---
 
 # DSL-437 — Benign participant activity and runtime execution semantics
@@ -22,6 +22,9 @@ Ordinary user and automation activity improves range realism, but benign simulat
 ## Traceability
 
 - DOCUMENTS → GITHUB_ISSUE `861` (DSL-437 — Deterministic live activity policy and target bindings)
+- DOCUMENTS → GITHUB_ISSUE `1122` (Predecessor-bound wall-readback concurrency regression)
+- DOCUMENTS → DOCUMENTATION `docs/decisions/issue-1122-dsl-437-wall-readback-concurrency-addendum.md` (Predecessor-bound wall-readback concurrency evidence)
+- TESTS → TEST `implementations/python/tests/test_dsl_437_benign_participant_execution.py` (Native participant scheduling, wall-paced advancement, and predecessor-bound readback)
 - CONSTRAINS → GITHUB_ISSUE `117` (Joint time semantics and language/runtime surfaces)
 - CONSTRAINS → GITHUB_ISSUE `118` (Time model contracts, conformance, and provenance)
 - CONSTRAINS → ADR `ADR-022` (Participant Behavior and Interaction Semantics)
diff --git a/implementations/python/tests/test_dsl_437_benign_participant_execution.py b/implementations/python/tests/test_dsl_437_benign_participant_execution.py
index cd2e319c..e2202eaf 100644
--- a/implementations/python/tests/test_dsl_437_benign_participant_execution.py
+++ b/implementations/python/tests/test_dsl_437_benign_participant_execution.py
@@ -2000,6 +2000,8 @@ def read_state() -> None:
     reader.start()
     assert time_runtime.read_entered.wait(timeout=1.0)
     predecessor = manager.snapshot
+    assert predecessor.time_model_state is not None
+    predecessor_coordinate = predecessor.time_model_state.clocks[policy.clock_address].coordinate
     time.sleep(0.1)
 
     assert manager.snapshot == predecessor
@@ -2010,7 +2012,7 @@ def read_state() -> None:
     assert not isinstance(outcome[0], Exception)
     state = outcome[0]
     assert isinstance(state, TimeRuntimeStateModel)
-    assert state.clocks[policy.clock_address].coordinate.tick == 0
+    assert state.clocks[policy.clock_address].coordinate == predecessor_coordinate
     assert manager.destroy().success