ADR 0012: Define PTO v0 ACRC service requests

Context

ACRC has an accepted 32-bit encoding and the trap catalog assigns SCALL (6), but the previous semantic handler only incremented a diagnostic epoch. It did not validate the request, save a return snapshot, route to a manager, or take the architectural trap. Bundle-control faults incorrectly occupied the same trap number before ADR 0010 corrected their identity.

Decision

ACRC request_type takes a synchronous trap immediately after the instruction:

• ACR1 accepts machine request 0 and security request 2; both route to ACR0.
• ACR2 through ACR15 accept machine request 0, system request 1, and security request 2. System request 1 routes to ACR1; the others route to ACR0.
• ACR0 and all other request values are illegal and raise ILLEGAL_INST (4).
• A valid request reports SCALL (6), records the four-bit request in the low CAUSE bits, and records the ACRC instruction TPC in TRAPARG0.
• Because ACRC is a 32-bit instruction, EBARG_TPC records the following instruction at source TPC + 4. Recovery therefore advances past ACRC unless manager software deliberately rewrites the visible resume word.
• A valid ACRC returns the internal scalar execution status Rejected because control transferred through a synchronous trap; no sequential dispatch update occurs after the trap handler vector is installed.

The ACR2 rule from the reconciled public contract is extended uniformly to the PTO v0 managed-ring range ACR2 through ACR15, consistent with ADR 0010.

Consequences

The SCALL trap identity now has an architectural producer. Request legality, routing, cause, argument, return snapshot, and recovery position are directly testable. The broader bundle rule requiring ACRC placement next to a terminator remains a bundle-formation closure target rather than an instruction-local effect.