[M1-SAMPLE-01] hello.laige (headless template)

[offdev]

Implements M1-SAMPLE-01 · hello.laige (headless template) per roadmap/M1-heartbeat.md.

The first complete Laige game — the headless template every game project (human or AI agent) starts from: one component, one system, one entity, deterministic by default, records and replays its own log.

What lands

• samples/hello/ — hello.cpp (99 code lines < the PRD §9.4 budget of 100; the NFR-13.5 "heavily commented" requirement lives in the ~76 comment lines, which don't count), config.json (canonical 60 Hz / 8-entity / 0x1F055EED / fpx16_16 config), hello.laige (provisional manifest — M3-ASSET-01 owns the real format), LICENSE, README.md (the full contract).
• The game — PlayerPos (M::Vec2, component + determinism marks at namespace scope), MovePlayer (LAIGE_SYSTEM; constant +1/tick per axis, wrapped in the [-16, 16] box), one entity at the box center. Config embedded in the binary; config.json is its declarative record (the hello_config_valid CTest runs laige-run --headless against it).
• The detcheck scenario contract — stdout = tick-0 line + one World::stateHash line per completed tick (301 lines at 300 ticks); stderr = engine logging + hello {headless|replay} ticks=N status=ok; exit 0/1/2.
• Replay — --replay LOG records its own run (debug builds only — parity with the engine's startReplayRecording policy; exit 2 under NDEBUG); --log LOG loads the log, checks the replay identity via replayIdentityDiff, and re-runs the log's frame count through the same tick loop. Record → replay is byte-identical. (laige-replay can't replay a game log — it registers only the built-ins — so the scenario binary carries the mode; noted in docs/api/replay.md.)
• CI — tests/sample/: 9 CTest entries (hello_scenario, hello_replay (Debug-gated), hello_replay_missing/_malformed, hello_mode_exclusive, hello_usage_unknown/_missing_value, hello_config_valid, hello_line_budget — a CMake-core code-line counter checked in CI per the step's Verify). The detcheck job's real-scenario step self-activates: both no-arg runs must exit 0 (M1-DET-04 swaps in the two-configuration comparison).
• Docs — detcheck.md (the real scenario now exists), replay.md (scope), building.md (command rows + target note), docs/README.md (M1 progress + link), ci.yml step comment.
• Roadmap — step checked; Progress Board M1 → 17/25 (also picks up the M1-DET-03 box that was checked without a board update); Change Log line.

Verification

• cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug + build warning-clean (-Wall -Werror); ctest 76/76 on the Debug tree (incl. the 9 hello entries) and 9/9 on a fresh ASan+UBSan tree (-DLAIGE_ASAN=ON).
• Release tree spot check: no-arg run exits 0, --replay exits 2 (the NDEBUG gate).
• The exact CI forms from the repository root: ./samples/hello/bin/hello (301 lines, exit 0) and ./build/bin/laige-detcheck --run-a=samples/hello/bin/hello --run-b=samples/hello/bin/hello (both exit 0, streams byte-identical).
• laige-determinism-lint OK (20 files, 0 violations), laige-include-lint OK (37 files, 1/10 vendored), api-manifest no drift (the sample adds no public header). No float/double tokens in the sample source.
• Untested locally: MSVC/AppleClang paths and the CI-only TSan lane (single-threaded binary; the ASan+UBSan run covers the memory side).

Compatibility

Additive only — no existing symbol, behavior, or CI gate changed.