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+// SPDX-License-Identifier: PMPL-1.0-or-later
+= `.affex` — AffineScript Face-Interop Manifest Specification v0.1
+:toc: macro
+:toclevels: 2
+:source-highlighter: rouge
+
+*Status*: Draft · Linked to requirements-target issue #84
+
+toc::[]
+
+== 1. Problem
+
+AffineScript supports multiple _faces_ — surface syntaxes that all lower to the
+same canonical AST. A programmer fluent in `canonical` reading a file written in
+`lucid` or `cafe` cannot tell what is going on, even though the semantics are
+identical.
+
+`.affex` is a *tooling-only, per-package manifest* that captures
+face-specific renderings of every top-level declaration, so readers can work in
+their preferred face without leaving their `.affine` files.
+
+== 2. Design decision: Shape 3 (face-interop manifest)
+
+The four speculative shapes from the issue were:
+
+[cols="1,3,2", options="header"]
+|===
+| # | Shape | Chosen?
+| 1 | Rosetta-stone side-by-side listing | Derived output only
+| 2 | Canonical-equivalence annotations | Not chosen
+| *3* | *Face-interop manifest* | *Primary form*
+| 4 | Mixed hand-written + auto | Supported (override blocks)
+|===
+
+*Why Shape 3*: the compiler already holds the canonical↔face bijection
+through the lowering pass. A manifest that captures this mapping once per
+package lets all tooling (LSP, CLI renderer, web viewer) derive any face view
+on demand — without storing N copies of source. Shape 1 (side-by-side listing)
+is a _derived view_ generated from Shape 3 + the source, not a stored artifact.
+
+== 3. File extension policy
+
+`.affex` files are *tooling artifacts only*. The compiler (`check`, `compile`,
+`eval`) does not parse or consume them. They are generated by the CLI and
+consumed by the LSP and renderer.
+
+Scope: *one `.affex` file per package*, placed at the package root alongside
+`dune` and the package's `.affine` source files.
+
+----
+src/
+  dune
+  pixi.affine
+  renderer.affine
+  pixi.affex          <- generated manifest for this package
+----
+
+== 4. File format
+
+`.affex` files are UTF-8 JSON with schema version `"affex/1"`.
+
+=== 4.1 Top-level structure
+
+[source,json]
+----
+{
+  "affex": "1",
+  "package": "affinescript-pixijs",
+  "generated_at": "2026-05-11T00:00:00Z",
+  "source_hash": "sha256:abc123...",
+  "faces": ["canonical", "lucid", "cafe"],
+  "mappings": [ ... ]
+}
+----
+
+[cols="1,1,3", options="header"]
+|===
+| Field | Type | Description
+| `affex` | `"1"` | Schema version. Must be `"1"` for this spec.
+| `package` | string | Package name (matches `dune` library name).
+| `generated_at` | ISO 8601 | Timestamp of last generation run.
+| `source_hash` | string | SHA-256 of all `.affine` source files combined, to detect staleness.
+| `faces` | string[] | Faces present in this manifest. Always includes `"canonical"`.
+| `mappings` | object[] | One entry per top-level declaration. See §4.2.
+|===
+
+=== 4.2 Mapping entry
+
+[source,json]
+----
+{
+  "id": "init_pixi",
+  "kind": "fn",
+  "source_file": "pixi.affine",
+  "canonical_span": { "start": [3, 1], "end": [5, 1] },
+  "faces": {
+    "canonical": {
+      "head": "pub fn init_pixi(width: Int, height: Int) -> Application",
+      "body_digest": "sha256:def456..."
+    },
+    "lucid": {
+      "head": "pub function init_pixi(width :: Int, height :: Int) :: Application",
+      "body_digest": "sha256:def456...",
+      "override": false
+    },
+    "cafe": {
+      "head": "pub init_pixi = (width: Int, height: Int) -> Application",
+      "body_digest": "sha256:def456...",
+      "override": true,
+      "override_source": "pixi.affex#overrides/init_pixi/cafe"
+    }
+  }
+}
+----
+
+[cols="1,1,3", options="header"]
+|===
+| Field | Type | Description
+| `id` | string | Canonical name of the declaration.
+| `kind` | `"fn"` \| `"type"` \| `"const"` \| `"effect"` \| `"trait"` \| `"impl"` | Declaration kind.
+| `source_file` | string | Relative path to the `.affine` file.
+| `canonical_span` | `{start: [line, col], end: [line, col]}` | Source location of the canonical declaration.
+| `faces.<name>.head` | string | Face-specific rendering of the declaration _signature_ (no body).
+| `faces.<name>.body_digest` | string | SHA-256 of the canonical body. Identical across faces — a mismatch signals the manifest is stale.
+| `faces.<name>.override` | bool | `true` if the face rendering was hand-written rather than auto-generated.
+| `faces.<name>.override_source` | string? | Pointer to the override block (§4.3) when `override` is `true`.
+|===
+
+*`head` only, not `body`*: the manifest stores _signatures_, not bodies. Full
+body rendering is done on demand by the renderer using the compiler's face
+lowering pass. This keeps the manifest compact and avoids duplicating source.
+
+=== 4.3 Override blocks
+
+When the auto-generated `head` for a face is wrong or unnatural, a developer
+can add a hand-written override in a top-level `"overrides"` section:
+
+[source,json]
+----
+{
+  "affex": "1",
+  ...
+  "overrides": {
+    "init_pixi": {
+      "cafe": "pub init_pixi: (Int, Int) -> Application"
+    }
+  },
+  "mappings": [ ... ]
+}
+----
+
+The generator preserves existing `overrides` on regeneration and merges them
+with newly auto-generated entries.
+
+== 5. Tooling
+
+=== 5.1 CLI commands
+
+==== Generate
+
+----
+affinescript affex generate [<package_dir>]
+----
+
+Reads all `.affine` files in `<package_dir>` (default: current directory),
+runs the face detection and lowering passes, and writes
+`<package_dir>/<package_name>.affex`. Existing override blocks are preserved.
+
+Options:
+
+* `--faces canonical,lucid,cafe` — limit faces to generate (default: all installed faces)
+* `--force` — regenerate even if source hash is unchanged
+
+==== Render
+
+----
+affinescript affex render --face <face> <file.affine>
+----
+
+Reads the package's `.affex` manifest, then renders `<file.affine>` in
+`<face>` to stdout. If no manifest exists, falls back to running the face
+lowering pass directly (slower).
+
+==== Diff
+
+----
+affinescript affex diff --face <face_a> --face <face_b> <file.affine>
+----
+
+Renders `<file.affine>` in both faces side-by-side (Shape 1 output) using the
+manifest as the source of truth.
+
+=== 5.2 LSP integration
+
+The LSP reads the nearest `.affex` manifest when opening a `.affine` file.
+When the user configures a preferred face (e.g. `"affinescript.face": "lucid"`
+in editor settings), hover tooltips, inlay hints, and the document outline
+render declaration signatures in that face rather than the source face.
+
+The LSP does not rewrite file contents — it only affects rendered metadata.
+
+== 6. Generation strategy
+
+[cols="1,2", options="header"]
+|===
+| Scenario | Approach
+| Clean package with no `.affex` | `affex generate` creates one from scratch
+| Source changed since last generate | `source_hash` mismatch; re-run `affex generate`
+| Override present for a declaration | Generator merges override, marks `"override": true`
+| New declaration added | Generator appends mapping; existing entries untouched
+| Declaration removed | Generator removes stale mapping entry
+|===
+
+*CI recommendation*: add `affinescript affex generate --check` (exits non-zero
+if manifest is stale) to CI for estates that adopt multi-face conventions.
+
+== 7. What this is NOT
+
+* Not a compiler concern. The compiler lowers all faces independently.
+* Not an AffineScript↔non-AffineScript FFI layer. See `extern fn` for that.
+* Not required for single-face estates. A project using only `canonical` has no
+  need for a `.affex` file.
+
+== 8. Open questions (pre-implementation)
+
+* [ ] Should `affinescript affex generate` be a separate binary or a subcommand of the main `affinescript` CLI?
+* [ ] Face names in the manifest should match exactly the values in `lib/face.ml`'s `face` type. Confirm the canonical string identifiers: `canonical`, `python`, `js`, `pseudocode`, `lucid`, `cafe`.
+* [ ] Should `head` rendering use the compiler's pretty-printer or store the raw source span? Raw source span is simpler and always correct; pretty-printed form is more useful when the source face differs from the reader face.
+* [ ] Staleness detection: `source_hash` over all `.affine` files in the package is coarse. Consider per-file hashes to support incremental regeneration.
+* [ ] Override syntax: embedding overrides inside the JSON file is workable but verbose. An alternative is a sidecar `.affex.overrides` file.
+
+== 9. Satisfaction criteria for closing #84
+
+This issue closes when Claude and the user explicitly agree, in a recorded
+exchange on this issue, that the following are satisfied:
+
+. This spec (or a revised version) is merged into `docs/specs/affex-spec.adoc`.
+. The file format schema (§4) is agreed to be correct and complete.
+. The tooling surface (§5) matches the CLI and LSP integration plan.
+. At least one of the open questions in §8 has a recorded resolution (or is
+  explicitly deferred with a rationale).
+
+_The presence of a PR, a draft, or a partial implementation does not satisfy
+these criteria alone — explicit mutual agreement in a comment on issue #84 is
+required._