diff --git a/.gitignore b/.gitignore
index 284dd33..31b24dd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,6 +17,7 @@ ai/reports/*.md
 # Local backend runtime data
 backend/runtime/
 backend/data/*.sqlite3
+backend/data/*.writer.lock
 !backend/data/.gitkeep
 backend/data/snapshots/**
 !backend/data/snapshots/.gitkeep
diff --git a/ai/tasks/done/TASK-140-fix-historical-runner-elo-import.md b/ai/tasks/done/TASK-140-fix-historical-runner-elo-import.md
new file mode 100644
index 0000000..ebf44f8
--- /dev/null
+++ b/ai/tasks/done/TASK-140-fix-historical-runner-elo-import.md
@@ -0,0 +1,103 @@
+---
+id: TASK-140
+title: Restore historical runner Elo imports
+status: done
+type: backend
+team: Backend Senior
+supporting_teams: [Arquitecto Python]
+roadmap_item: foundation
+priority: high
+---
+
+# TASK-140 - Restore historical runner Elo imports
+
+## Goal
+
+Restore `historical-runner` startup by fixing the Elo/MMR model import contract used by `app.elo_mmr_engine`.
+
+## Context
+
+The advanced `historical-runner` service runs `python -m app.historical_runner --hourly` and intentionally imports `rebuild_elo_mmr_models`. The engine imports scoring constants from `app.elo_mmr_models`, but that module no longer exports every constant required by the engine.
+
+## Steps
+
+1. Inspect the listed files first.
+2. Restore the missing Elo/MMR model/config constants in the correct module.
+3. Keep the change narrow and avoid disabling the runner or Elo/MMR silently.
+4. Validate the backend, RCON data pipeline, integration tests, advanced Compose services and relevant HTTP endpoints.
+
+## Files to Read First
+
+- `ai/architecture-index.md`
+- `ai/repo-context.md`
+- `ai/orchestrator/backend-senior.md`
+- `backend/app/historical_runner.py`
+- `backend/app/historical_ingestion.py`
+- `backend/app/elo_mmr_engine.py`
+- `backend/app/elo_mmr_models.py`
+- `backend/app/elo_mmr_storage.py`
+
+## Expected Files to Modify
+
+- `backend/app/elo_mmr_models.py`
+- `.gitignore`
+- `ai/tasks/done/TASK-140-fix-historical-runner-elo-import.md`
+
+## Constraints
+
+- Do not remove or disable `historical-runner`.
+- Do not disable Elo/MMR silently.
+- Do not modify frontend files.
+- Do not reintroduce Comunidad Hispana #03.
+- Do not commit runtime database files.
+- Preserve RCON ingestion, AdminLog materialization, recent matches, match detail and scoreboard candidate backfill.
+
+## Validation
+
+- `python -m compileall backend/app`
+- `powershell -ExecutionPolicy Bypass -File scripts/run-rcon-data-pipeline-tests.ps1`
+- `powershell -ExecutionPolicy Bypass -File scripts/run-integration-tests.ps1`
+- `docker compose --profile advanced up -d --build backend frontend historical-runner rcon-historical-worker`
+- `docker compose --profile advanced ps`
+- `docker compose logs --tail=100 historical-runner`
+- `Invoke-WebRequest "http://localhost:8000/health" | Select-Object -ExpandProperty Content`
+- `Invoke-WebRequest "http://localhost:8000/api/historical/recent-matches?server=all-servers&limit=20" | Select-Object -ExpandProperty Content`
+
+## Outcome
+
+Implemented the import-contract fix by restoring the missing Elo/MMR model constants exported from `backend/app/elo_mmr_models.py`:
+
+- `ELO_K_FACTOR`
+- `MIN_VALID_PLAYER_PARTICIPATION_SECONDS`
+- `MIN_VALID_PLAYER_PARTICIPATION_RATIO`
+
+The constants live with the rest of the Elo/MMR model thresholds, preserving the existing `app.elo_mmr_engine` import boundary and avoiding any silent disabling of the runner or Elo/MMR. `.gitignore` now also ignores `backend/data/*.writer.lock` because advanced Compose validation creates the shared SQLite writer lock as runtime state.
+
+Validation completed:
+
+- `python -m compileall backend/app`
+- Direct imports of `app.historical_runner`, `app.historical_ingestion` and `app.elo_mmr_engine`
+- `powershell -ExecutionPolicy Bypass -File scripts/run-rcon-data-pipeline-tests.ps1`
+- `powershell -ExecutionPolicy Bypass -File scripts/run-integration-tests.ps1`
+- `docker compose --profile advanced up -d --build backend frontend historical-runner rcon-historical-worker`
+- `docker compose --profile advanced ps`
+- `docker compose logs --tail=100 historical-runner`
+- `Invoke-WebRequest "http://localhost:8000/health" | Select-Object -ExpandProperty Content`
+- `Invoke-WebRequest "http://localhost:8000/api/historical/recent-matches?server=all-servers&limit=20" | Select-Object -ExpandProperty Content`
+- `Invoke-WebRequest "http://localhost:8080/historico.html?nocache=runner" | Select-Object -ExpandProperty StatusCode`
+
+Manual verification:
+
+- `historical-runner` stayed `Up` in the advanced profile.
+- `rcon-historical-worker` stayed `Up`.
+- `historical-runner` logs showed `historical-refresh-loop-started` and no `ImportError`.
+- `/health` returned `status: "ok"`.
+- `/api/historical/recent-matches` returned RCON-backed recent match data.
+- `historico.html` returned HTTP 200.
+- No frontend files were modified.
+- No runtime database files were staged or committed.
+
+## Change Budget
+
+- Prefer fewer than 5 modified files.
+- Prefer changes under 200 lines when feasible.
diff --git a/backend/app/elo_mmr_models.py b/backend/app/elo_mmr_models.py
index 652e27e..e07d2e3 100644
--- a/backend/app/elo_mmr_models.py
+++ b/backend/app/elo_mmr_models.py
@@ -14,8 +14,11 @@ ACCURACY_APPROXIMATE = "approximate"
 ACCURACY_PARTIAL = "partial"
 
 DEFAULT_BASE_MMR = 1000.0
+ELO_K_FACTOR = 60.0
 MIN_VALID_MATCH_DURATION_SECONDS = 900
 MIN_VALID_MATCH_PLAYERS = 20
+MIN_VALID_PLAYER_PARTICIPATION_SECONDS = 900
+MIN_VALID_PLAYER_PARTICIPATION_RATIO = 0.45
 FULL_QUALITY_PLAYER_COUNT = 70
 FULL_QUALITY_DURATION_SECONDS = 3600
 MONTHLY_MIN_VALID_MATCHES = 5