diff --git a/docs/architecture/README.md b/docs/architecture/README.md
index ad24fae..3d5dc0e 100644
--- a/docs/architecture/README.md
+++ b/docs/architecture/README.md
@@ -45,7 +45,7 @@ format definition; the engine is generic.
 | [008](decisions/008-reject-tunion-in-aligned-mode.md) | Reject TUnion in Aligned Mode for v1 | Unions are the protocol pattern; aligned-mode union semantics were broken |
 | [009](decisions/009-builder-api.md) | Builder API for Schema Construction | Fluent Rust API producing `serde_json::Value`; covers BAST kinds + standard JSON Schema; resolves OQ-003. *Output format amended to BAST / standard JSON Schema by ADR-BAST.* |
 | [010](decisions/010-generalized-validation-validate-bytes.md) | Generalized Validation — `validate_bytes` on `AlkTypeEngine` | Single-call binary-buffer validation; materialize `Value` from bytes, then validate. *Validation step amended to the BAST-native validator by ADR-VAL-SPLIT.* |
-| [011](decisions/011-compiled-read-plan-for-packed-mode.md) | Compiled Read Plan for Packed Mode | `ReadPlan` — the packed read-side compiled form, symmetric to `OffsetMap` (aligned) and `PackedLayout` (packed write). Closes review #004's 400x read-path gap; retires ADR-007's "re-parse on demand" framing. *Proposed.* |
+| [011](decisions/011-compiled-read-plan-for-packed-mode.md) | Compiled Read Plan for Packed Mode | `ReadPlan` — the packed read-side compiled form, symmetric to `OffsetMap` (aligned) and `PackedLayout` (packed write). Closes review #004's 400x read-path gap; retires ADR-007's "re-parse on demand" framing. *Accepted.* |
 
 ## Relevant Open Questions
 
diff --git a/docs/architecture/decisions/011-compiled-read-plan-for-packed-mode.md b/docs/architecture/decisions/011-compiled-read-plan-for-packed-mode.md
index bacdb98..30d912b 100644
--- a/docs/architecture/decisions/011-compiled-read-plan-for-packed-mode.md
+++ b/docs/architecture/decisions/011-compiled-read-plan-for-packed-mode.md
@@ -2,8 +2,11 @@
 
 ## Status
 
-Proposed — for review. Closes review #004 H1 + M1 + L1 + L2;
-retires the "re-parse on demand" framing from ADR-007.
+Accepted. Closes review #004 H1 + M1 (packed side) + L1 + L2;
+retires the "re-parse on demand" framing from ADR-007. A derisking
+POC on branch `readplan-poc` confirmed the `ReadPlan` shape covers
+every `BastType` arm in the current read loop before implementation
+began (see "POC coverage" at the end).
 
 ## Context
 
@@ -108,8 +111,10 @@ A pre-resolved tree of read instructions. Every `$ref` is resolved, every
 endianness is computed (field override or container default), every
 union variant is inlined. The read loop indexes into a `Vec`, matches
 on a `ReadKind`, and calls `data_access::read_*` with a precomputed
-`Endian` — no `resolve_typeref`, no JSON node access, no `format!`
-allocations.
+`Endian` — no `resolve_typeref`, no `BastDef::parse`, no JSON node
+access on the happy path. (`format!` for error-path attribution may
+still occur on the error path; it does not run on the happy path and
+is not the cost being removed here.)
 
 ```rust
 pub struct ReadPlan {
@@ -187,10 +192,18 @@ as `AlkTypeError::Schema` — the same untrusted-input discipline
 stores `Arc<ReadPlan>`. `sequential_reader()` returns
 `SequentialReader { plan: Arc::clone(&self.plan), .. }` — an owned
 reader (ADR-007's factory decision is retained; the reader owns its
-cursor, shares the immutable plan). The `bast_doc: Value` clone
-(`src/engine.rs:85`) is no longer needed on the packed read path; the
-engine retains it only for `validate_bytes`'s materialize-then-validate
-flow if the plan doesn't subsume that path (see Scope below).
+cursor, shares the immutable plan).
+
+`bast_doc: Value` (`src/engine.rs:85`) is retained on the engine
+unconditionally. In packed mode it becomes unused by the read path
+(both `sequential_reader` and `validate_bytes` consume the plan);
+in aligned mode it is still needed for `read_field`/`write_field`/
+`validate_bytes`. Keeping it always avoids a mode-conditional field
+and costs only a `Value` clone paid once at `compile`. `ReadPlan`
+must be `Send + Sync` so `Arc<ReadPlan>` can be shared from the
+`Send + Sync` engine (ADR-007); this falls out naturally from the
+plan being immutable owned data, but the implementation should add a
+`static` bound assertion test to lock it in.
 
 ### Public API change (breaking — version bump to 0.3.0)
 
@@ -266,9 +279,13 @@ The crate is pre-1.0 with two in-house downstream consumers
   precomputed `Endian`." The expected per-chunk cost is in the
   hand-rolled codec's ballpark (the `data_access` calls are the same
   ones the hand-rolled codec makes).
-- **Closes M1's packed-side re-parses for free.**
-  `validate_bytes` (packed) and `materialize_packed` both consume the
-  `ReadPlan` — no re-parse on either path.
+- **Closes M1's packed-side re-parse (`engine.rs:284`, `validate_bytes`).**
+  The aligned-side M1 sites (`engine.rs:334,467`,
+  `layout_builder.rs:190`) are deliberately left as-is — they are not
+  hot for the packed-codec use case, and Option A remains available as
+  an additive later fix if an aligned-mode hot loop ever emerges. This
+  is a reversible bet, not a claim that the aligned-side M1 is a
+  non-issue.
 - **Unifies the two packed read-side consumers on one compiled form.**
   `SequentialReader` and `materialize_packed` walk the same `ReadPlan`,
   mirroring how `OffsetMap` unifies the aligned read and write sides.
@@ -286,14 +303,14 @@ The crate is pre-1.0 with two in-house downstream consumers
   (refcount bump). The plan is immutable and shared across all readers
   from one engine. ADR-007's "owned fresh reader" decision is retained;
   the reader owns its cursor, shares the plan.
-- **Determinism.** `ReadPlan::compile` is a pure function of the BAST
-  document + root name — same input, same plan. This makes the
-  "compiled form" visibly deterministic, opening a future capability:
-  fingerprinting the plan (e.g., `#[derive]` a hash) for cross-run
-  caching, disk-cached compiled plans, or schema-version handshakes
-  for `alkcall`'s hub/spoke topology. Not implemented now, but the
-  compiled form makes it possible; a re-parse-per-field design makes
-  it invisible.
+- **Deterministic compile.** `ReadPlan::compile` is a pure function of
+  the BAST document + root name — same input, same plan. This makes the
+  "compiled form" visibly deterministic, which is a prerequisite for
+  future capabilities (fingerprinting the plan for cross-run caching,
+  disk-cached compiled plans, or schema-version handshakes for
+  `alkcall`'s hub/spoke topology). Not implemented in this ADR and not
+  needed to justify the decision; listed here only so a future ADR
+  doesn't re-derive the prerequisite. See "Future capabilities" below.
 - **Retires the "re-parse on demand" framing (L2).** ADR-007's "Cost"
   section and `src/engine.rs:112-115`'s doc comment framed re-parse as
   the intended design. With the plan, the read path never re-parses;
@@ -312,15 +329,18 @@ The crate is pre-1.0 with two in-house downstream consumers
   in-house downstream consumers, both updated with the bump. The
   breakage is smaller than review #004's Option A (no `Bast*` type
   changes — `BastDoc` stays borrowed, stays the validation-side tree).
-- **Two type walkers in the crate.** `BastDoc` (validation, aligned
-  one-shot paths) and `ReadPlan` (packed read path) coexist. This is
-  the same structural split as `OffsetMap`/`PackedLayout` (different
-  compiled forms for different modes/sides), not a duplication: each
-  compiled form serves its mode/side pair, and `BastDoc` serves the
-  paths that don't have a compiled form yet (validation, aligned
-  one-shot reads/writes). A future cleanup can give the aligned
-  one-shot paths their own compiled form; it is additive, not
-  blocking.
+- **A parallel typed tree, not a flat lookup table.** This is the
+  honest cost. `OffsetMap` and `PackedLayout` are flat `(path, range)`/
+  `(path, position)` projections of `BastType`; `ReadPlan` is a full
+  parallel hierarchy (`CompositePlan` mirrors `BastType`'s
+  Struct/Union/Array/Record). The maintenance tax is real and higher
+  than those: when schema semantics change, `BastDoc`/`BastType` and
+  `ReadPlan`/`CompositePlan` move together. It is worth it because the
+  perf win on composite-heavy schemas (the SFTP-shaped union-with-`$ref`
+  -variants packet) justifies it — see the next bullet. This is a
+  permanent tax accepted in exchange for a ~20–50x composite-dispatch
+  win on top of the 400x re-parse fix, not a structural symmetry with
+  the flat compiled forms.
 - **Eager `$ref` resolution at compile time.** `ReadPlan::compile`
   resolves all `$ref`s eagerly, including union variant refs. This is
   correct (the schema is fixed at compile time) and matches the
@@ -426,4 +446,45 @@ closes L2. L1 falls out at step 2. The aligned-side M1 paths
   access-time check
 - [ADR-010](010-generalized-validation-validate-bytes.md) —
   `validate_bytes` (packed) consumes the `ReadPlan` via
-  `materialize_packed`
\ No newline at end of file
+  `materialize_packed`
+
+## Future capabilities (not part of this ADR)
+
+The deterministic-compile property of `ReadPlan` is a prerequisite for
+several capabilities that are explicitly out of scope here but worth
+naming so a future ADR doesn't re-derive the prerequisite:
+
+- Fingerprinting the plan (e.g. `#[derive(Hash)]`) for cross-run
+  caching of compiled plans.
+- Disk-cached compiled plans (skip `compile` on warm start).
+- Schema-version handshakes for `alkcall`'s hub/spoke topology —
+  peers exchange plan fingerprints instead of full BAST documents.
+- A `WritePlan` and/or `ValidationPlan` that follow the same
+  compile-once-walk-many pattern for the deferred M1 sites
+  (`engine.rs:334,467`, `layout_builder.rs:190`, `bast_validation`).
+
+None of these justify this ADR; the 400x read-path gap does. They are
+listed only as forward references.
+
+## POC coverage
+
+Before this ADR was accepted, a derisking POC on branch `readplan-poc`
+walked the read loop against every `BastType` arm in
+`src/sequential_reader.rs:303-381` (and the parallel arms in
+`materialize.rs`) and confirmed the `ReadPlan`/`CompositePlan`/
+`ReadKind`/`DiscriminatorPlan` shape covers all cases, including the
+two spots where a plan arm could subtly miss a case:
+
+- **Union discriminator split (`Byte` vs `Field`).** Both are covered:
+  `DiscriminatorPlan::Byte { offset, disc_type }` and
+  `DiscriminatorPlan::Field { name, field_index }`. The field-name case
+  pre-resolves the discriminator field's `ReadKind` so dispatch reads
+  it from the plan, not from a re-parsed `BastField`.
+- **Array variable-element-stride (`element_stride = 0`).** Covered:
+  `CompositePlan::Array { element, count, element_stride }` preserves
+  the `0`-signals-variable convention, and the read loop walks
+  sequentially when `element_stride == 0` (matching today's
+  `walk_variable_array_size`).
+
+The POC also confirmed `ReadPlan: Send + Sync` holds for the planned
+shape (immutable owned data, no interior mutability, no lifetimes).
\ No newline at end of file