12. Error Codes (Normative)

FACET reserves F000–F999 for standard diagnostics. Host extensions must use X.<host>.<code>.

Parse / syntax

• F001 invalid indentation (must be 2 spaces)
• F002 tabs forbidden
• F003 malformed syntax / invalid token / invalid escape / unclosed structure
• F402 attribute interpolation forbidden (``)

Semantic / type

• F401 variable not found
• F405 invalid variable path (missing field)
• F451 type mismatch
• F452 constraint violation / unsupported construct / invalid placement / invalid signature
• F453 runtime input validation failed (@input)
• F454 policy deny (deterministic)
• F455 guard undecidable (fail-closed)
• F456 missing/invalid effect declaration

Graph / imports

• F505 cyclic dependency in R-DAG
• F601 import not found / disallowed path
• F602 import cycle

Runtime / mode / layout / gas

• F801 prohibited I/O or construct disallowed by profile/mode
• F802 unknown lens
• F803 pure-mode cache miss for Level-1 lens
• F901 critical overflow in Token Box Model
• F902 gas exhausted

Fast troubleshooting map

• Parse issues first (F001/F002/F003)
• Then placement/schema (F452)
• Then types (F451/F453)
• Then dependency graph (F401/F405/F505)
• Then runtime mode/policy (F801/F803/F454/F455/F902)