Read-only native observer build

The no-save playthrough reads original Civilization II 1.06 data with the Windows 3.1 ToolHelp MemoryRead API. The helper is a separate hidden Win16 program. It does not patch CIV2.EXE, write game memory, select units, or issue gameplay commands. Its fixed mailbox accepts a nonce rather than an arbitrary address. The Python decoder applies the same own/visible-state filtering as the debug save decoder before model requests.

First fetch the hash-pinned original runtime, then build the helper:

python3 scripts/fetch_runtime.py
python3 scripts/build-observer.py

Docker must support Linux amd64 containers. The build uses:

Input	Pinned value
Compiler	Official Open Watcom 2.0 Linux x64 installer, September 14, 2026 build
Compiler SHA-256	b51ad127b52c44ddcc9451e4960674b9b31b1457b84c798521dcf3f84c494273
Container	debian@sha256:88200866dfff7ea7f5cbcb6ec7c8a701889efe6fe859fe64d6990e4b07ea4171, platform linux/amd64
Helper source SHA-256	ce82cdd26379bdd2817fb1fd87b34474a21753b3a043046dcdee84da74760dc5
Compiled helper SHA-256	b2ca27df1f3c15d6cdbcc8411be761e4d96fd018425bc23c65df329490432236
Original CIV2.EXE SHA-256	b5a64ecbd8ebdd37e3ca2391c57319fec7ac227fcd2c3b9c96498969ea51ef96

Current-build is a mutable upstream URL. A different download is rejected. If it has moved, supply an existing copy of that exact official installer with --compiler-archive PATH; the checksum is still mandatory. There is no automatic fallback to another compiler. The Open Watcom distribution has its own license; the compiler is not vendored into this repository.

The script extracts only the required compiler headers, libraries, and Linux tools under ignored .runtime/observer-build/. Every cached toolchain file is compared against the pinned installer. Compilation runs without container network access and with read-only source/toolchain mounts:

wcl -bt=windows -ms -zW -fe=civ2obs.exe /src/civ2_observer.c toolhelp.lib

The resulting binary must equal the calibrated helper hash. A source or compiler change requires a separately reviewed calibration and pin update.

The script writes ignored engine/game/civ2-win31-observer.zip. Compared with the downloaded original archive, it adds CIV2OBS.EXE and changes only the empty WINDOWS/WIN.INI load entry to load=c:\CIV2OBS.EXE. It then checks every decompressed archive member: all other original bytes, including CIV2.EXE, Windows binaries, game rules and artwork, must remain identical. The original archive is retained. Build provenance is written to ignored engine/game/observer-build.json. Do not publish either game archive, Windows files, compiler bundle, or private observation capsules.

A runtime boot with observer: true selects this private archive. Fresh setup supports:

python3 -m civ2.boot --port 3930 --profile final-001 --directory .runtime/final-001-setup --no-saves

Use a fresh dedicated runtime, with the local server/browser already connected. Setup makes the original menu selections, explicitly disables Autosave each turn, and verifies all eleven Game Options checkboxes. It reads the untouched initial state through the observer and writes host-side initial-observation.json and image evidence. This command never invokes the game's Save dialog. The original game may create its startup autosave before the preference can be changed; its presence must be declared in the campaign's starting file inventory. From the verified setup boundary onward, the live observer rejects a new or changed game save. The requirement is no saves during the playthrough, not a claim that the original installation has no pre-existing .SAV files.

load_setup_report(directory, require_no_saves=True) checks the packaged images, native initial-state capsule, original settings, and explicit autosave-off readback before the campaign copies them into its audit journal. Image capture and these host-side evidence files are observations, not game saves.