96 lines
2.8 KiB
Markdown
96 lines
2.8 KiB
Markdown
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# FCS/1 — Function Composition Schema (Execution-Only)
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Status: Approved
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Owner: Architecture
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Version: 1.0.0
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SoT: Yes
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Last Updated: 2026-02-21
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Linked Phase Pack: PH07
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Tags: [execution, descriptor, deterministic]
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**Document ID:** `FCS/1`
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**Layer:** L2 — Function descriptor schema for deterministic execution
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**Depends on (normative):**
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* `DDS` — canonical FCS/1 v1-min TLV layout and validation rules
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* `PCB1` — parameter block encoding rules (DDS §7.3)
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* `ASL/1-CORE v0.4.x` — logical value model (`Artifact`, `Reference`)
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---
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## 0. Purpose & Scope
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`FCS/1` defines the **execution-only** descriptor schema for composite and
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custom functions. It explicitly excludes policy, intent, scope, authority, and
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other governance metadata (those belong in `FCT/1`).
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`FCS/1` descriptors are immutable and content-addressed; identical descriptors
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MUST hash to identical CIDs.
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---
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## 1. Descriptor Model (logical)
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An `FCS/1` descriptor captures the deterministic execution recipe:
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```
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FCSDescriptor {
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function_ptr : CID // FPS/1 primitive or nested FCS/1 descriptor
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parameter_block : CID // PCB1 parameter block
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arity : uint32
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}
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```
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* `function_ptr` MAY reference another `FCS/1` descriptor (composition), or a
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primitive function descriptor (e.g., `FPS/1`).
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* `parameter_block` MUST reference a valid PCB1 payload.
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* `arity` defines the expected number of input slots (must match PCB1).
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---
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## 2. Canonical Encoding (v1-min)
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The canonical byte encoding for `FCS/1` descriptors is defined by DDS §7.2:
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* COR/1 framing with strict TLV order.
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* Required TLVs only: `function_ptr (0x30)`, `parameter_block (0x31)`,
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`arity (0x32)`.
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No other TLVs are permitted in v1-min.
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---
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## 3. Validation Rules
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Implementations MUST reject descriptors that violate any of the following:
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1. TLVs are not in strict ascending order, or appear more than once.
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2. `parameter_block` does not decode as a valid PCB1 envelope.
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3. `arity` does not match PCB1 slot manifest length.
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4. The descriptor graph (following nested `function_ptr` references) is cyclic.
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5. Any legacy or unknown governance TLV appears.
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Error mapping follows DDS (e.g., `ERR_FCS_TAG_ORDER`, `ERR_FCS_PARAMETER_FORMAT`,
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`ERR_PCB_ARITY_MISMATCH`, `ERR_FCS_CYCLE_DETECTED`, `ERR_FCS_UNKNOWN_TAG`).
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---
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## 4. Composition Semantics
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* Composition is **pure**: a descriptor that references another `FCS/1`
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descriptor inherits its deterministic execution recipe.
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* The composed descriptor graph MUST be acyclic.
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* Registries MUST admit only canonical, validated `FCS/1` descriptors.
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---
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## 5. Conformance
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An implementation is **FCS/1–conformant** if it:
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* Accepts only v1-min canonical encodings.
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* Enforces the validation rules in §3.
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* Treats descriptors as immutable and content-addressed.
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* Rejects any descriptor with policy/intent metadata embedded.
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