Make path/component validation errors contextual

uid: ISS-0025 status: BACKLOG priority: medium owner_role: REWORK estimate: TBD dependencies: [] risk: medium milestone: backlog

Category

REWORK

Evidence

• src/filare/models/utils.py:119-125 raises "{filename} does not exist." or "{filename} is not a file." without showing cwd or the referencing YAML field, making it hard to locate the bad path.
• src/filare/models/harness.py:323-338 raise generic Exception strings for mismatched types in connections/templates without quoting the designator or the type mismatch details.
• src/filare/models/harness_quantity.py:55-63 raises ValueError when quantity_multipliers.txt JSON is invalid but does not echo the file path or the malformed content that failed.

Suggested Next Steps

1. Include full resolved path and caller context in path errors, e.g., image 'docs/img/missing.png' not found (cwd=/app, referenced by connector X1.image).
2. Replace generic connection/type errors with value-aware ValueError messages: connections[1] uses template 'W1' as connector but expected connector template; check metadata/templates.
3. When parsing quantity_multipliers.txt, echo the file path and JSON error: invalid JSON in outputs/quantity_multipliers.txt: Expecting value at line 1 column 5; delete or fix the file to re-prompt.
4. Add regression tests that provoke each error and assert the improved messaging without altering behavior.