docs: 100% proto2 + proto3 conformance

README status table: replace the four \"deferred\" rows with
explicit checkmarks for groups, extensions, closed enums; bump
both conformance lines to 2806 and 434 successes. Note MessageSet
as the only known gap (protoreflect rejects upstream, our vendored
proto2 schema has those four nested messages stripped).

docs/codegen.md proto2-support section gets three subsections —
Groups, Extensions, Closed enums — each describing the runtime
surface a user touches (decode_group, _extensions, the closed flag).
The descriptor-table example includes a group field and the new
extensions_by_id / extensions_by_full_name indices.

PLAN.md M9 closes with the conformance numbers; M5 header updated
to reflect that proto2 is no longer deferred.

docs: proto2 is supported for the core surface

README's status table swaps the single \"proto2 deferred\" row for
four entries that name what works (required / optional / custom
defaults / packed semantics) and what doesn't (extend, extensions,
group, MessageSet) so users can decide before they generate.

docs/codegen.md replaces the proto2 deferral section with a
\"Proto2 support\" page: the three new descriptor attributes
(required, default_value, optional everywhere), the existing
IsPacked() trick that already produces the right unpacked default,
and a concrete list of the four features that still refuse to
generate (with the MessageSet upstream-rejection caveat).

PLAN.md gains M9 — Proto2 baseline. Wire format, codecs, parser,
dynamic, tests are checked off; extend / group / MessageSet stay
open because the conformance schema needs all three and they're
each their own slice.

docs: full reference + how-to set, migrate Makefile to Justfile

Documentation overhaul that adds the missing user-facing surface:
four reference pages (runtime-api, generated-api, cli, grpc-contract),
twelve how-tos walking from first-message through custom transports,
a troubleshooting page, and a docs/index map. Every how-to references
a runnable artifact under examples/, all of them verified end-to-end.

Build system migration: the Makefile is gone; the Justfile is now
the canonical entry point and absorbs every target. examples/Justfile
ships one recipe per runnable example, forwarded via top-level
'just examples <name>'. The 'examples are part of the documented
surface' convention is pinned in CLAUDE.md, alongside a dedicated
section on updating the conformance harness (PROTOBUF_TAG bumps,
libjsoncpp path drift, new test-category wiring).

Stale-number sweep across README/PLAN/CLAUDE: fixture count 18→10,
test count 613/130→639, wire.lua LOC dropped, M7 marked done.
Descriptor-shape block deduplicated against codegen.md as the
canonical source. gRPC transports spec status reframed from
'draft / decision deferred' to 'shipped contract; external
transports deferred'.

.gitignore picks up *.snap / *.xlog / *.vylog / *.run / *.pid /
512.lock so example state can't leak into the working tree.

codegen: emit strict <Type>_fields / _oneofs constants for lazy view

Lazy-view callers passing a typo'd field name to :get / :has / :set /
:clear / :which got `nil` back, indistinguishable from a legitimately-
absent optional field. Failures surfaced as missing data downstream.

Each generated message now exports a M.<Type>_fields table mapping
each field name to itself (and M.<Type>_oneofs for oneof groups),
wrapped by a new pb.field_names() helper that errors on unknown-key
reads and on any write. Routing field-name arguments through these
tables turns a typo into a load-time error at the read site.

Eager _encode / _decode keep round-tripping plain Lua tables — the
constants table is a lazy-view contract, documented in
docs/api-modes.md. README and lazy_test.lua converted to the new
pattern; three new tests cover typo / read-only / oneof-typo errors.

docs: drop text-format parser handoff brief

The pb.text.decode slice landed (7ec8f2b); the handoff brief is no
longer load-bearing. Removes the file and unlinks references from
README.md and PLAN.md.

docs: spec out msgpack encoding and gRPC transport story

Two design slices captured under docs/specs/ for later pickup:

- msgpack_encoding.md: proto schemas as IDL, msgpack as wire format.
  Default mp_map keyed by field number; ARRAY/MP_TUPLE opt-ins for
  box.space feeders; WKT bridging to MP_DATETIME / MP_INTERVAL.
- grpc_transports.md: Connect-JSON over HTTP/1.1 as default external
  transport, net.box tunnel for in-cluster, explicit no on HTTP/2
  termination (recommend Envoy). Conformance anchored on
  connectrpc/conformance — same framed-runner shape as the existing
  protobuf conformance harness.

PLAN.md cross-links both specs from M4, Open Questions, and Non-goals.

docs: refresh README + PLAN; add api-modes and codegen notes

README.md
  * Status table reflects current state: text-format encode + decode,
    -0.0 preservation, strict FieldMask, all-green proto3 conformance.
  * Conformance baseline jumped to 1493 / 416 / 0 failures (was
    1389 / 0 / 79 in the old table); explains the 1313+18 skipped
    tests are all TestAllTypesProto2, deferred separately.
  * Layout walks the full runtime/pb/ tree (lazy, text, json, wkt,
    grpc, parser, dynamic, fileset, descriptor_pb).
  * Generated API section calls out the three-mode design and links
    to docs/api-modes.md and docs/codegen.md.

PLAN.md
  * Section 2 ("Current state") rewritten — no longer claims M0;
    lists what's actually in the codebase.
  * M1, M2, M3 marked done with [x] checkboxes (had stale [ ]
    markers across items that have been shipping for months).
  * M5 conformance numbers updated to current baseline; calls out
    the three commits that closed the proto3 suite (text decode,
    -0 codec, JSON strict pass).
  * M7 text-format parser entry updated: 416 ✓ / 0 failures (was
    406 / 10 expected before the codec -0 fix).
  * Added an M7 entry for the JSON strict-validation pass (six
    classes of relaxation now enforced).

docs/api-modes.md (new)
  * When to use full vs runtime (descriptor / reflect) vs lazy.
  * Concrete code shapes for each, plus what the generated
    Person_encode actually looks like in full mode.
  * Descriptor-shape contract that ties all three together.
  * Lazy: SoA index rationale, sparse-read vs dense-read trade-offs,
    cross-over points from bench numbers.

docs/codegen.md (new)
  * Pipeline diagram, CLI options, what gets emitted per .proto.
  * Walk through the inline (full) mode emission with annotated
    generated code.
  * Runtime mode: pb.finalize_message's per-field writer/reader
    closures and why they exist.
  * Hot-path rules the generated code observes (no pairs(), 64-bit
    as cdata, SoA over AoS for large index structures, keep hot
    helpers small).
  * Plugin source map; where to extend for a new wire type.
  * Proto2 deferral section: what it would take and why we punt.

docs: handoff brief for the pb.text.decode slice

Self-contained brief targeting the 408 proto3 TextFormatInput tests
still skipped after the encoder + SGROUP work. Covers existing
surface (text.lua encode-only, parser.lua schema parser, conformance
dispatch), grammar buckets the suite exercises (10 categories with
upstream test counts), files to touch, LuaJIT/cdata/box.NULL
conventions, and a verifying-locally checklist. Suggested
recursive-descent shape mirrors runtime/pb/parser.lua's cursor
mechanics.

No code changes; positions the next slice without committing to a
specific implementation schedule.