MGS1052: a model tier declaration cannot be used

magus stops loading a workspace when a magus\job.modelTiers or magus\job.modelTier call cannot be used as written:

• tiers is not an enum, or the enum has no cases;
• default is not a case of that enum;
• a key in hosts is not the harness id that magus\harness.provider returns, or names a harness the magusfile did not wire;
• hosts, bounds or skills raises, or answers a case with the wrong type, an empty model alias, a negative bound, or two cases the same alias on one host;
• magus\job.modelTier is not given a function;
• a call is made twice, or from a project's magusfile instead of the root one.

The error names the call and the case it failed on.

Why

A declaration that failed to register would leave a workspace that reads as tiered while every job gets the default, and a mapping that names a harness nothing wired would pick no model at all. Both stay invisible until a job runs, so the load refuses instead.

Resolution

• Declare an enum and pass it. enum ModelTier { economy, standard, principal }, cheapest first, then magus\job.modelTiers(ModelTier, default: ModelTier.standard, ...).
• Key hosts by the harness. Keep what magus\harness.provider returns when you wire the harness, and use it as the key.
• Cover every case. Write hosts, bounds and skills as exhaustive match expressions, so a tier added to the enum fails magus check until each covers it.
• Call each member once, in the root magusfile.
• Turn tiers off with magus\job.modelTiers(null) when the workspace wants none.

See model tiers.