@@ -26,13 +26,13 @@ The protocol uses no words or alphabet, but four meaning-free local symbols. For
 See [`docs/results-ecp6.md`](docs/results-ecp6.md) for the conclusion, [`docs/protocol-specification-ecp6.md`](docs/protocol-specification-ecp6.md) for the wire format and [`evidence/ecp6/report.md`](evidence/ecp6/report.md) for the compact confirmatory evidence.
 
 ECP-7 development now tests how much of that result depends on the explicit
-one-factor-per-slot architecture. Its first seven sealed batches are valid
+one-factor-per-slot architecture. Its first eight sealed batches are valid
 negative results. Straight-through hard utilization remains the best weakly
 structured population-validation result at 1.92%. A parallel joint-context
 sender increased code use to 3,118–3,415 messages and train exactness to 9.60%,
-but shape remained below chance and validation stayed at 0.51%. The ECP-6
-positive controls remained perfect. The ECP-7 confirmatory test remains sealed.
-See
+but shape remained below chance and validation stayed at 0.51%. Adding relaxed
+context invariance reduced that gain. The ECP-6 positive controls remained
+perfect. The ECP-7 confirmatory test remains sealed. See
 [`docs/development-log-ecp7.md`](docs/development-log-ecp7.md).
 
 ## Build on this work
@@ -80,6 +80,7 @@ Do not translate those artifacts in place. New experiment configurations and all
 - [`config/ecp7-b5-development.yaml`](config/ecp7-b5-development.yaml) — straight-through sender consensus on the Batch 3 base.
 - [`config/ecp7-b6-development.yaml`](config/ecp7-b6-development.yaml) — normalized minimax factor reconstruction on the Batch 3 base.
 - [`config/ecp7-b7-development.yaml`](config/ecp7-b7-development.yaml) — bounded parallel generation from one shared joint context.
+- [`config/ecp7-b8-development.yaml`](config/ecp7-b8-development.yaml) — algebraic context invariance on the parallel sender.
 - [`config/ecp7-positive-control-development.yaml`](config/ecp7-positive-control-development.yaml) — ECP-6 positive control on the ECP-7 split.
 - [`config/ecp0.yaml`](config/ecp0.yaml) — machine-readable configuration from step 1.
 - [`config/ecp1.yaml`](config/ecp1.yaml) — frozen configuration of the population trial.
 
@@ -0,0 +1,18 @@
+extends: ecp7-b7-development.yaml
+
+experiment:
+  title: ECP-7 parallel sender with context-invariant transitions
+  arm: parallel_sender_algebraic_consistency
+  objective: >-
+    Test whether making the same atomic meaning change produce the same relaxed
+    message displacement across training contexts converts the parallel
+    sender's memorized distinctions into a compositional protocol.
+
+training:
+  algebraic_consistency:
+    enabled: true
+    weight: 1.0
+    warmup_steps: 800
+    relaxed_temperature: 1.0
+    batch_size: 32
+    quadruple_pool_size: 8192
@@ -41,7 +41,7 @@ python3.12 -m venv .venv
 .venv/bin/ecp6 --config config/ecp6.yaml validate
 ```
 
-Expected baseline: 68 passing tests and split sizes `14336/1024/1024`.
+Expected baseline: 70 passing tests and split sizes `14336/1024/1024`.
 
 ## 4. Reproduce ECP-6
 
@@ -71,7 +71,7 @@ This reruns a known experiment. It must not be presented as a new independent co
 
 ## 5. Continue ECP-7 scientifically
 
-Do not modify ECP-0 through ECP-6 or the completed ECP-7 Batch 1 through Batch 7
+Do not modify ECP-0 through ECP-6 or the completed ECP-7 Batch 1 through Batch 8
 configs. ECP7-B1-I collapsed to 130–139 hard messages. ECP7-B2-I improved its
 soft objective but collapsed further to 85–104 hard messages. ECP7-B3-I applied
 that loss to straight-through hard messages and improved to 585–972 messages,
@@ -84,12 +84,14 @@ remained near chance and validation reached only 0.46%. All paired ECP-6
 positive controls stayed perfect. ECP7-B7-I replaced autoregression with a
 parallel joint-context sender. It increased train exactness to 9.60% and used
 3,118–3,415 messages, but shape stayed below chance and validation reached only
-0.51%. The confirmatory ECP-7 test is still sealed.
+0.51%. ECP7-B8-I added context-invariant atomic transitions, but regressed to
+857–1,135 messages and 0.32% validation. The confirmatory ECP-7 test is still
+sealed.
 
 Continue with this sequence:
 
 1. Read `docs/research-design-ecp7.md` and `docs/development-log-ecp7.md`.
-2. Define exactly one ECP7-B8 intervention and its failure criterion.
+2. Define exactly one ECP7-B9 intervention and its failure criterion.
 3. Register the variant and immutable configuration hashes before training.
 4. Add tests for every new invariant.
 5. Use only `smoke` and `develop`; keep the ECP-7 test split sealed.
@@ -103,20 +105,20 @@ Continue with this sequence:
 ## 6. Recommended next experiment
 
 Batch 7 is the strongest optimization result but still memorizes rather than
-composes: train exactness and code-space use increased sharply, while held-out
-color-shape exactness remained low. The most informative next step is one
-context-invariance objective on the parallel sender. A clean ECP7-B8
-progression is:
+composes. Batch 8 context invariance suppressed that gain. B7 messages change
+when shape changes, and its fresh universal translator decodes shape better
+than its jointly trained recurrent receivers. The most informative next step is
+one generic decoder change. A clean ECP7-B9 progression is:
 
 - keep the same world and bit budget;
 - keep the joint autoregressive sender and generic isolated receiver;
-- keep the B7 sender and receiver, then add the existing algebraic consistency
-  loss for identical atomic factor transitions across different contexts;
+- keep the B7 sender and losses, then replace the GRU final-state decoder with
+  one position-aware MLP over all four embedded message slots;
 - measure injectivity, validation composition and new-reader induction;
 - rerun the ECP-6 architecture as the frozen positive control.
 
-Do not restore the Batch 4, Batch 5 or Batch 6 terms, and do not combine
-context-invariance with receiver changes, architectural resizing, longer
+Do not restore the Batch 4 through Batch 6 or Batch 8 terms, and do not combine
+the receiver change with sender changes, architectural resizing, longer
 training, variable-length messages or negotiation. That would make its effect
 uninterpretable.
 
 
@@ -490,3 +490,75 @@ context-invariance objective: the existing algebraic consistency loss for the
 same atomic factor transition in two different training contexts. This directly
 targets composition rather than memorization and assigns no factor to a message
 slot. It must not restore B4–B6 losses or change the receiver simultaneously.
+
+## Batch 8 preregistration
+
+Date: July 18, 2026<br>
+Seed: `11`<br>
+Maximum population steps: `5,000`<br>
+Split-SHA-256: `4947058c75ab07cb43a87eb82776b12cb2a7e2eeba7114de110d3b852cbc64cd`<br>
+Test unsealed: **no**
+
+ECP7-B8-I retains the complete Batch 7 architecture and loss set, then activates
+one context-invariance term. It matches two training-only instances of the same
+atomic factor transition and minimizes the squared difference between their
+relaxed message displacements. Its fixed construction and hyperparameters are
+recorded in `docs/research-design-ecp7.md`. No factor is assigned to a channel
+slot. The unchanged positive control is rerun. Smoke is mechanical only and
+cannot authorize tuning.
+
+## Batch 8 results
+
+Positive-control run: `runs/ecp7-batch8-control-development/20260718T120358Z-ecp7-development`<br>
+Intervention run: `runs/ecp7-batch8-intervention-development/20260718T120358Z-ecp7-development`<br>
+Test unsealed: **no**
+
+| Metric | Positive control | ECP7-B8-I |
+|---|---:|---:|
+| Population train, mean | 100% | 0.5349% |
+| Population train, worst link | 100% | 0.4464% |
+| Population validation, mean | 100% | 0.3235% |
+| Population validation, worst link | 100% | 0.0977% |
+| Universal translator, validation | 100% | 0.6836% |
+| Exact sender-message agreement | 100% | 1.18% |
+| Unique messages per sender | 15,360 | 857–1,135 |
+| Collision meanings per sender | 0 | 14,225–14,503 |
+| Message entropy | 13.91 bits | 8.23–8.92 bits |
+| Development gate | pass | **fail** |
+
+The positive control again validated the batch at 100%. ECP7-B8-I failed the
+population, validation, translator and injectivity gates. It stopped at step
+2,200 under the unchanged early-stopping rule, with step 600 selected.
+
+At that checkpoint, algebraic consistency loss was `0.05265` at its scheduled
+weight of `0.75`, and the hard-utilization loss was `-0.7321`. The surrogate
+could be reduced, but it did not create a useful discrete compositional code.
+Compared with B7, training exactness fell from 9.5965% to 0.5349%, unique
+messages fell from 3,118–3,415 to 857–1,135, population validation fell from
+0.5066% to 0.3235%, and translator validation fell from 2.7588% to 0.6836%.
+
+Population validation factor accuracies were approximately
+`[7.63%, 6.57%, 89.04%, 96.64%]`. The context objective therefore suppressed
+the strong B7 color signal and left shape near chance. Universal-translator
+factor accuracies of `[14.60%, 10.30%, 98.12%, 99.02%]` again show that a fresh
+decoder extracts more color and shape information than the jointly trained
+population receivers, but far below the registered gate.
+
+Both sealed analyses report 65 matching artifact hashes, 16,384 validation-only
+episodes, no confirmatory-test keys, valid local alphabets, and exactly 14
+declared bits for every logged message.
+
+## Batch 8 decision
+
+ECP7-B8-I is recorded as a negative development result and is not retained.
+Relaxed transition invariance competed with the discrete task and utilization
+objectives instead of converting B7's distinctions into composition. The
+confirmatory split remains sealed.
+
+B7 remains the strongest optimization base. Its shape minimal pairs change
+approximately 1.11–1.13 message positions and concentrate about 64% of that
+change in one position, while its post-hoc universal translator decodes shape
+better than the jointly trained receivers. A future ECP7-B9 may keep the B7
+sender and losses but replace the recurrent final-state receiver with one
+generic position-aware MLP over all four embedded slots. This tests decoder
+access without factor-to-slot binding and must not add another loss.
@@ -356,3 +356,44 @@ All existing validity and development gates remain unchanged. Failure is
 recorded without confirmatory test access. No receiver change, hidden-size
 change, extra loss, longer duration or alternative parallel architecture may be
 tried inside Batch 7.
+
+## Batch 8 preregistration — Algebraic context invariance
+
+Status: **preregistered for sealed development**<br>
+Preregistered: July 18, 2026<br>
+Configuration: `config/ecp7-b8-development.yaml`<br>
+Raw configuration SHA-256: `3eac0d25bf636d4a1aeb6161ad479a4a78f0a3e88788a0274c154c21ff192829`<br>
+Effective configuration SHA-256: `6e8f9ea0e968693bd9f67a4ca1180ab447c6e2d6c2fbc6b9f9a66582aa02fa3c`
+
+Batch 7 greatly improved training exactness and code-space use, but those
+distinctions did not compose across the held-out color-shape matching. Batch 8
+retains the entire B7 architecture and loss set, then activates one existing
+context-invariance objective that was previously disabled.
+
+Every training quadruple contains meanings `A`, `B`, `A'`, and `B'`. The
+transitions `A→A'` and `B→B'` change the same factor value in two different
+contexts, and all four meanings belong to the training split. For relaxed
+message distributions `m`, the objective is:
+
+`L_alg = mean ||(m(A') - m(A)) - (m(B') - m(B))||²`
+
+This encourages the same atomic semantic change to produce the same message
+displacement regardless of the other factor values. It uses factor identities
+only to construct matching transitions. It does not specify a target message,
+symbol, channel slot, factor-to-slot binding or codebook.
+
+The loss weight is fixed at `1.0` with an 800-step linear warmup, relaxed
+temperature `1.0`, 32 quadruples per update and a deterministic pool of 8,192
+training-only quadruples. These values match the dormant inherited settings;
+only `enabled` and `weight` change from B7. The parallel sender, generic
+receiver, hard-utilization loss, channel, split, training duration, selection
+and translator remain unchanged.
+
+The batch contains exactly two seed-11 runs:
+
+1. the unchanged ECP-6 positive control;
+2. ECP7-B8-I with algebraic context invariance on the B7 parallel sender.
+
+All existing validity and development gates remain unchanged. Failure is
+recorded without confirmatory test access. No alternative quadruple sampling,
+weight, warmup, receiver, architecture or duration may be tried inside Batch 8.
@@ -43,6 +43,10 @@ sender. It reached 3,118–3,415 messages, 9.60% train exactness and 45.64% colo
 accuracy, but shape remained below chance and validation stayed at 0.51%. Exact
 identities and hashes are in `batch7-manifest.json`.
 
+Batch 8 added algebraic context invariance to Batch 7. The relaxed surrogate
+improved, but the discrete protocol regressed to 857–1,135 messages and 0.32%
+validation. Exact identities and hashes are in `batch8-manifest.json`.
+
 Reproduce the development arms with:
 
 ```bash
 
@@ -0,0 +1,41 @@
+{
+  "batch": "ECP7-B8",
+  "confirmatory_test_unsealed": false,
+  "control": {
+    "artifact_hashes": {
+      "effective_config.yaml": "4bfb976293f117d3ae35f790e4fd6371628be95d91febb334bc275dc5d6b66d4",
+      "posthoc-analysis.json": "f22ba2bf1042a97deb5274f03fab22d70678d1418986927764ced363634e0846",
+      "seed-11/metrics.json": "e9bde51415a531c0ad32f7caf921048840dff9c1f6d55b1ad4635292ff668b60",
+      "summary.json": "ad2301a93c46c175d2b38687dfe7b66e8b75a14e02b8971fdf18a8a30d3273ae"
+    },
+    "development_gate_passed": true,
+    "population_train_mean_exact_match": 1.0,
+    "population_validation_mean_exact_match": 1.0,
+    "run_id": "20260718T120358Z-ecp7-development",
+    "universal_translator_validation_exact_match": 1.0,
+    "unique_messages_per_sender": [15360, 15360, 15360, 15360]
+  },
+  "intervention": {
+    "artifact_hashes": {
+      "effective_config.yaml": "15fa04bb33b321b2ca8c29f01da84ff8bbcdd70e85ecbe96c08d6a51cca84cef",
+      "posthoc-analysis.json": "4f1af42cbd75044cd7149a729a4869d81b55a3c3e8b929da0a08570d0e608c60",
+      "seed-11/metrics.json": "945cf063cb1300029175a590452d7e2f39e1ff068b6eb423892357f15581c745",
+      "summary.json": "7fefb6774ba89d3300aaa2138640057484181591940ce918c27349a5e1fa17ff"
+    },
+    "best_algebraic_consistency_loss": 0.05264976993203163,
+    "best_code_utilization_loss": -0.7321186661720276,
+    "best_step": 600,
+    "development_gate_passed": false,
+    "exact_sender_message_agreement": 0.011827256944444446,
+    "message_entropy_bits_per_sender": [8.229443275271354, 8.409431758360435, 8.922917128759757, 8.81365004262187],
+    "population_train_mean_exact_match": 0.005349295479910714,
+    "population_validation_factor_accuracy": [0.0762939453125, 0.065673828125, 0.890380859375, 0.9664306640625],
+    "population_validation_mean_exact_match": 0.00323486328125,
+    "run_id": "20260718T120358Z-ecp7-development",
+    "universal_translator_validation_exact_match": 0.0068359375,
+    "unique_messages_per_sender": [857, 895, 1123, 1135]
+  },
+  "seed": 11,
+  "split_artifact_sha256": "676195997ee0c77d5c9565bae045dbb938b432a2e4e74b666233b0a41f924718",
+  "split_sha256": "4947058c75ab07cb43a87eb82776b12cb2a7e2eeba7114de110d3b852cbc64cd"
+}
@@ -19,7 +19,7 @@
     PopulationSystem,
     Receiver,
     ReceiverModel,
-    Sender,
+    SenderModel,
     make_receiver,
     make_sender,
 )
@@ -756,7 +756,7 @@ def build_algebraic_quadruples(
 
 
 def algebraic_consistency_loss(
-    sender: Sender, quadruples: Tensor, *, temperature: float
+    sender: SenderModel, quadruples: Tensor, *, temperature: float
 ) -> Tensor:
     """Make the same factor change context-invariant in message distribution."""
     if quadruples.ndim != 3 or quadruples.shape[1:] != (4, 4):
 
@@ -78,3 +78,8 @@ def ecp7_b6_config():
 @pytest.fixture(scope="session")
 def ecp7_b7_config():
     return load_config(PROJECT_ROOT / "config" / "ecp7-b7-development.yaml")
+
+
+@pytest.fixture(scope="session")
+def ecp7_b8_config():
+    return load_config(PROJECT_ROOT / "config" / "ecp7-b8-development.yaml")
@@ -297,3 +297,34 @@ def test_ecp7_b7_changes_only_the_sender_generation_architecture(
     assert "joint_message_collision" not in b7_training
     assert "sender_message_consensus" not in b7_training
     assert "factor_minimax" not in b7_training
+
+
+def test_ecp7_b8_adds_only_algebraic_context_invariance(
+    ecp7_b7_config, ecp7_b8_config
+):
+    assert ecp7_b8_config["world"] == ecp7_b7_config["world"]
+    assert ecp7_b8_config["dataset"] == ecp7_b7_config["dataset"]
+    assert ecp7_b8_config["channel"] == ecp7_b7_config["channel"]
+    assert ecp7_b8_config["agents"] == ecp7_b7_config["agents"]
+    b7_training = deepcopy(ecp7_b7_config["training"])
+    b8_training = deepcopy(ecp7_b8_config["training"])
+    assert b7_training.pop("algebraic_consistency") == {
+        "enabled": False,
+        "weight": 0.0,
+        "warmup_steps": 800,
+        "relaxed_temperature": 1.0,
+        "batch_size": 32,
+        "quadruple_pool_size": 8192,
+    }
+    assert b8_training.pop("algebraic_consistency") == {
+        "enabled": True,
+        "weight": 1.0,
+        "warmup_steps": 800,
+        "relaxed_temperature": 1.0,
+        "batch_size": 32,
+        "quadruple_pool_size": 8192,
+    }
+    assert b8_training == b7_training
+    assert "joint_message_collision" not in b8_training
+    assert "sender_message_consensus" not in b8_training
+    assert "factor_minimax" not in b8_training