# Research Notes

Engineering findings, negative results, and design decisions that would otherwise be lost. Every one
was learned by **probe or execution**, not assumption, and every one is recorded so it is not
rediscovered.

**Status tags:** `MEASURED` · `RESOLVED` · `REJECTED` · `OPEN` · `ATTEMPTED`.

---

## 1. Findings that changed the code

### F4-1 — the MiniLM tokenizer ceiling (`MEASURED`)

The MiniLM tokenizer's own ceiling is **256** (verified by probe). This project truncates to **128** —
a deliberate truncation *well inside* the ceiling, not the model limit. Satellite queries are short;
halving the sequence halves attention cost for no measurable accuracy loss. The encoder **asserts**
`max_length ≤ 256`, because truncating above the ceiling is a **silent no-op**.

**Consequence:** `router.max_length: 128` with an assertion, rather than a comment.

### F4-2 — the router needs no GPU (`MEASURED`)

The encoder is frozen, so embeddings are **cached** and the 50,822-parameter adapter trains on cached
vectors. **Measured on CPU: 20 epochs / 4,096 vectors in 0.28 s.**

**Consequence:** the router can be retrained during development without a GPU.

### F4-3 — splits must be by group (`MEASURED`)

Splits are by **group** (template / hard-negative family), never by example. Hard-negative families
are placed in the **test** split so their accuracy measures generalisation rather than memorisation.
Splitting by example would leak template variants across the boundary and inflate the score.

### F5-1 — `AutoModelForVision2Seq` does not exist (`MEASURED`)

In transformers 5.17.0, `AutoModelForVision2Seq` **does not exist** (it is not merely deprecated);
`AutoModelForImageTextToText` is present.

**Consequence:** the loader is resolved by **feature detection**, never hardcoded to one class name.

### F5-2 — the processor cost overrun is ~17×, not 4× (`MEASURED`)

The processor's default `longest_edge` is **2048**, which upscales a 512-px tile **4×** and then
splits it (`do_image_splitting=True`) into sub-images:

| Setting | `pixel_values` | prompt tokens |
|---|---|---|
| default | `(1, 17, 3, 512, 512)` | 1142 |
| pinned (`processor_longest_edge: 512`) | `(1, 1, 3, 512, 512)` | — |

The plan estimated a 4× cost overrun; the real figure is **~17×**. The value **must** be set
explicitly on the processor at construction time, and `core/config.py` now **enforces**
`processor_longest_edge <= image.tile_size` so the pin is a control rather than a comment.

### F5-3 — prompts must go through the chat template (`MEASURED`)

SmolVLM requires one `<image>` token per image in the prompt. Hand-written prompt strings raise
`ValueError`.

**Consequence:** prompts are always built through `processor.apply_chat_template()`, enforced by the
config key `vlm.prompt_must_use_chat_template: true`.

### P7-1 — the RemoteCLIP projected dimension is 512 (`MEASURED`)

The RemoteCLIP ViT-B/32 transformer width is **768**, but `visual.proj` maps to a **projected** dim of
**512**. The grounding head's per-cell feature is therefore `4 × 512 = 2048`.

**Consequence:** `grounding.encoder_projected_dim: 512` is declared in config so `core/config.py` can
validate the head **without importing torch**, and `specialists/grounding/remoteclip.py` asserts the
same value against the real model at load time.

### C-1 — the availability mask is consumed by the head, not by CROMA (`MEASURED`)

CROMA always sees the canonical channel counts (12 optical, 2 SAR). The availability mask is applied
by the **fusion head** (`input_dim = 3 × 768 + 12 + 2 = 2318`), not by the encoder.

### C-6 — T4 is SM 7.5, so training uses fp16, not bf16 (`MEASURED`)

`training.precision: fp16` because the target GPU (T4) is compute capability 7.5; bf16 is unavailable
there. The loader validates the value is one of `fp16|bf16|fp32`.

### C-7 — `image_resolution % 8 == 0` (`MEASURED`)

CROMA requires `image_resolution % 8 == 0`. The native value **120** yields 225 patches. Enforced at
config load.

### C-8 — ZeroGPU does not support `torch.compile` (`MEASURED`)

`torch.compile` must never be enabled on the (historical) ZeroGPU target. Enforced: the loader
**fails startup** if `deployment.torch_compile` is true.

### C-9 — STANet hyperparameters are upstream-verified (`MEASURED`)

Change detection uses a STANet-style architecture with upstream-verified hyperparameters: ResNet-18
encoder, **PAM** self-attention mode, tile 256, threshold 0.50, BCE 0.5 + Dice 0.5.

---

## 2. The grounding resolution decision — a pre-registered rejection (`REJECTED`)

**Question:** should grounding decode at 448 or 224?

**Answer: 224. 448 was rejected** — notable because the rejection was *pre-registered* and then
*confirmed* by a paired test over identical samples (n = 16,159):

| Comparison (448 vs 224) | Value |
|---|---|
| mean best IoU | **−0.0147** |
| recall@0.5 | −0.0022 |
| recall@0.10 | −0.0699 |
| recall@0.25 | −0.0243 |
| latency | **1.59×** |
| paired mean difference | −0.0147 |
| paired 95 % CI | **[−0.0160, −0.0134]** |
| paired t | **−22.63** |
| 448 better on | 8.5 % of records |
| 448 worse on | **20.9 %** of records |

448 lost on **every** axis. The pre-registered decision rule and the paired test **agree** on 224.
This is the model for how a resolution decision should be made: declared in advance, then tested.

---

## 3. The router defect — a real bug, found and fixed (`RESOLVED`)

### 3.1 Symptom

The query *"Where are the built-up areas in this image?"* collapsed to **`vqa`** and answered
**"River"** — instead of routing to `grounding`. A second query, *"Where is the new airport?"*,
behaved the same way.

### 3.2 Root cause

Two functions with different information:

- **`interpret()`** — produces the console's *reading*; **asset-count-blind** (text only).
- **`chooseTask()`** — performs *dispatch*; **asset-count-aware**.

The defect was in the dispatch path's handling of spatial/lexical cues, so region queries fell through
to the generic VQA specialist.

### 3.3 Fix and verification

The fix was deployed to `SatQuery-Frontend` and validated by **three independent live passes**:

| Pass | Deployed HEAD | Result |
|---|---|---|
| 1 | `ff46eba42b18` + `d413d3672311` | 8/8 |
| 2 | `2d7ae53b482d` | 8/8 |
| 3 | `2d7ae53b482d` | 8/8 |

Both defect queries now dispatch to `grounding`:

| Query | Run id | Dispatched |
|---|---|---|
| Where are the built-up areas in this image? | `run_467ffa406f22` | `grounding` |
| Where is the new airport? | `run_46980ba55c62` | `grounding` |

**24 live runs, 24 correct dispatches, 0 mock nodes.** Screenshots are in
[`../screenshots/`](../screenshots/).

---

## 4. The harness false-positive — caught before it could lie (`RESOLVED`)

An earlier live-validation harness typed queries with **synthetic CDP key events**, which Chrome
**silently drops when the window lacks OS focus**. The harness therefore dispatched the page's
*default* query and still recorded a "result" — a **false pass**.

**Fix:** the current harness **asserts form state before dispatch** (`q_ok`, `obs_ok`, `t0_ok`) and
uses deterministic query entry (`js()` value-set + `type_text()` via CDP `Input.insertText`).

**Independent check:** the earlier 8/8 run was re-examined and confirmed **not** infected — its
answers were query-specific and the query text was embedded in the answers. The failure mode is
recorded because it is exactly the silent false-positive an evaluation harness must never have.

---

## 5. The `transport_mode: auto` fallthrough (`OPEN`)

`SATQUERY_TRANSPORT=auto` tries the tunnel, then falls through to the forward path on timeout. The
forward path to a **private** repo returns `302` quickly, but the wake step still consumes
`SATQUERY_WAKE_TIMEOUT_S` (120 s) first — so a worst-case failed request takes ≈ **249 s**
(150 + 120). This is the root shape of the observed transient tunnel gap.

A patch adding `forward_unavailable` (503) and `upstream_timeout` (504) codes plus the
`codespace_name` `.strip()` fix was authored and verified (`py_compile` clean). **Status: OPEN — the
patch is prepared but NOT deployed.**

---

## 6. The `interpret()` / `chooseTask()` asymmetry — intentional (`RESOLVED`)

For *"What changed between the earlier and later image?"* with **one** asset attached, the console
**reads** `change` while dispatch correctly falls back to **`change_vqa`**. This is not a bug: the
reading describes the question's intent; the dispatch respects what can actually be computed with the
assets present. It is documented so it is not mistaken for a defect.

---

## 7. Environment findings (would otherwise cost hours)

| Finding | Detail |
|---|---|
| **Dead proxy in the authoring sandbox** | outbound calls need `--noproxy '*'` (curl) or `ProxyHandler({})` (Python). |
| **The sandbox proxy is slow for uploads** | `huggingface_hub` uploads stalled at ~51 kB/s through `http_proxy=127.0.0.1:58294`; the fix is to unset `http_proxy`/`https_proxy` and set `no_proxy='*'`. |
| **`hf_hub_download` returned an EMPTY file** | sha256 `e3b0c442…` (the empty-content hash), which produced a **false FAIL** for all six artifacts. The honest check is a direct HTTPS download with `ProxyHandler({})`. |
| **pytest is only in the repo venv** | `.venv/Scripts/python.exe`; a bare `pytest` misses it. |
| **The full test suite trips a bulk-delete guard** | sandbox-specific; affects `test_safe_delete_shim`. |
| **Cloudflare `_headers` concatenate** | two matching rules are merged, not overridden; Chromium takes the **first** `max-age`. |
| **Cloudflare 308-redirects `X.html` → `/X`** | reference the extensionless path. |
| **A forwarded Codespace port returns `302`** | for a private repo — this is *why* the tunnel exists. |
| **Chrome drops synthetic CDP key events without OS focus** | the harness false-positive (§4). |
| **`browser-use` block-buffers stdout** | even when redirected; needs explicit line buffering to stream. |

---

## 8. The BigEarthNet format contradiction (`ATTEMPTED`, reported not resolved)

The BigEarthNet data format **contradicts the original plan**. This was **reported rather than
silently patched**, because quietly changing the preprocessing would move the frozen config hash.

Two facts matter:

1. The BigEarthNet documentation — its uses, mentions, or endorsements — does **not** specify a
   percentile stretch. This project nevertheless applies percentile normalisation (2/98) for optical
   inputs to match the CROMA contract. That is a **deliberate, documented choice**, not an upstream
   fact.
2. The local subset is **100 % single-label**, against the official 1–11 multi-label scheme, so
   metrics computed on it are **not comparable** to published multi-label numbers.

---

## 9. Where the evidence lives

| Topic | Evidence |
|---|---|
| Findings F4-1…F5-3, C-1…C-9, P7-1 | `docs/PHASE*.md`, `docs/ARCHITECTURE_*.md`, `docs/CROMA_NORMALISATION_UPSTREAM_EVIDENCE.md` |
| The 448-vs-224 paired test | `docs/PHASE7_RESOLUTION_DECISION.md` |
| The VLM rejection | `docs/PHASE6_RUN1_REJECTION_DIAGNOSIS.md`, `artifacts/vlm/phase6_closure.json` |
| Router defect + 3 live passes | `.workbuddy-ai/scratch/live_validation/` (`run_output.txt`, `run_final2.txt`, `run_final3.txt`) |
| The undeployed B-07 patch | session scratch `fix-b07-forward-unavailable.patch` |
| Live validation harness | `.workbuddy-ai/scratch/run_all_postfix2.harness`, `recompute_verdicts.py` |