feat(fuzz): cargo-fuzz workspace, 3 wire-surface targets; bump alkcall 0.8.1

- Bump alkcall 0.8.0 -> 0.8.1 (duplicate adopt/open channel-state
  destruction fix from alkcall's fuzz campaign; AGENTS.md stale-pin fix).
- Adopt fuzzing per docs/plans/fuzzing.md (mirrors alkcall's
  docs/research/fuzzing.md as-built layout): fuzz/ workspace with own
  [workspace] table, nightly pinned for the subtree only, invariant
  logic in a stable-toolchain shared crate.
- Targets: chunk_frame (5-byte chunk codec), negotiation_frame
  (negotiation framing + NegotiateRequest + error_response_bytes +
  the cross-codec peek-disambiguation seam), control_json
  (ControlMessage JSON + signal_from_name). src/local/ out of scope
  (not wire-attacker-shaped).
- 328 committed seeds (deterministic generator); grown corpora
  gitignored. Corpus replay on stable is the standing fuzz gate
  (cargo test --manifest-path fuzz/shared/Cargo.toml).
- Detached-runner rule (fuzz/run-detached.sh): campaigns never run in
  the foreground of an agent session - OOM in a target must cost the
  fuzzer, never the session host.
- Root Cargo.toml gained [workspace] members/exclude (MSRV vs fuzz
  nightly dev-deps footgun) and fuzz/ in the publish exclude.

Verification: cargo test (113), cargo test --all-features (156),
clippy stable + wasm32-unknown-unknown, fmt, doc, publish dry-run,
corpus replay 328 seeds - all green. 10-min detached campaigns on all
three targets: 0 crashes/hangs/OOMs/leaks (chunk_frame cov-saturated
at 710 edges; negotiation_frame 3.69M execs cov 3157; control_json
8.6M execs cov 2035). Corpus replay caught three harness-model
mismatches pre-campaign (payload-slice shape; the negotiation framing
layer is length-prefix-only - Json unreachable from read_frame;
zero-length frames admitted by the reader, rejected by the adapter's
parse). Campaigns recorded in docs/plans/fuzzing.md section 8.

AGENTS.md

@@ -238,6 +238,7 @@ cargo clippy --all-targets -- -D warnings
 cargo fmt --check
 cargo doc --no-deps
 cargo test --all-features
+cargo test --manifest-path fuzz/shared/Cargo.toml    # fuzz corpus replay — the standing fuzz gate
 cargo check --target wasm32-unknown-unknown       # the default crate stays wasm-clean
 cargo clippy --target wasm32-unknown-unknown -- -D warnings
 cargo publish --dry-run --allow-dirty             # before a release
@@ -248,6 +249,13 @@ wasm-clean" invariant — run it whenever a non-`local` module changes.
 `cargo test --all-features` exercises the `local` backend (PTY mode is
 `#[cfg(unix)]`; pipe mode is cross-platform).
 
+The fuzz corpus replay (`docs/plans/fuzzing.md`) runs every committed
+seed through the same invariant functions the cargo-fuzz targets run —
+on stable, no nightly needed. Run detached campaigns
+(`fuzz/run-detached.sh <target>` — never foreground fuzzing) before a
+release and after touching `src/wire.rs`, `src/negotiation.rs`,
+`src/control.rs`, the adapter, or the session pump.
+
 ## Architecture Context
 
 - `docs/plans/project-setup.md` — the current plan (phases 0–5). All
@@ -312,11 +320,9 @@ wasm-clean" invariant — run it whenever a non-`local` module changes.
   `BiStream`, `BidiStreamSource`, `AuthContext`, `Identity`,
   `IdentityProvider`, `AccessControl`, `OwnershipProvider`,
   `OwnershipStore`, `InMemoryOwnershipStore`, `HandlerError`,
-  `StreamError`) come from `alkcall::core`. alkcall is v0.4.x —
-  breaking changes are expected at this major-zero stage; this is the
-  first real consumer, so we find and fix issues upstream rather than
-  working around them. Pin `alkcall = "0.6.0"` (the
-  establishment-plan payload — ADR-049 amendment 2, review 007 R-01;
-  adopted by alktty ADR-010 §2A — allocation runs in the channels
-  establisher, the `TtyHandle` crosses via the plan) and bump
-  deliberately.
+   `StreamError`) come from `alkcall::core`. alkcall is v0.8.x —
+   breaking changes are expected at this major-zero stage; this is the
+   first real consumer, so we find and fix issues upstream rather than
+   working around them. Pin `alkcall = "0.8.1"` (0.8.1 fixes the
+   duplicate adopt/open channel-state destruction found by alkcall's
+   fuzz campaign) and bump deliberately.