# Cross-representation tachograph event mixing fix

## Problem

When a runtime request combined `TACHOGRAPH_FILE_SESSION` and `TACHOGRAPH_DB`, CARD and VU observations of the same tachograph fact were often not fused. The old compatible keys embedded representation-specific values such as tenant metadata, coordinate string scale, country representation, region defaults, vehicle completeness and interval metadata.

Examples of equivalent values that produced different keys:

- country `13` versus `D`;
- region `0` versus `null`;
- longitude `9.3883333333333336` versus `9.388333333333334`;
- file-session package tenant `default` versus the DB tenant;
- CARD events without VIN versus VU events with VIN.

## Changes

- Compatible activity and support keys now contain only stable candidate identity:
  - driver;
  - domain;
  - event type;
  - semantic lifecycle;
  - exact event timestamp.
- Exact timestamp behavior is unchanged.
- Added `RuntimeEventEvidenceCompatibilityMatcher` to validate grouped candidates semantically.
- Support compatibility normalizes:
  - tachograph nation numeric/alpha forms;
  - region `0`/blank/null;
  - coordinate decimal scale with a `1e-9` serialization tolerance;
  - registration formatting;
  - optional VIN, odometer and operation data.
- Missing optional data is enrichable, while conflicting meaningful values prevent fusion.
- Activity compatibility allows source-specific optional metadata differences while still checking tenant, vehicle/registration and card slot compatibility.
- Mixing now evaluates compatibility per primary/secondary pair instead of suppressing every secondary in a broad group.
- Internal mixing state now tracks events by object identity and uses the UUID before `externalSourceEventId`, avoiding collisions from repeated source-side IDs such as `CARDPLACE-1`.

## Tests

Added regression coverage for:

- file-session `CARD_PLACE` versus DB `VU_PLACE` with `13`/`D`, `0`/null and decimal-scale differences;
- file-session CARD activity versus DB VU activity;
- meaningful coordinate conflicts remaining separate.