Task #222 partial — unblock AB Legacy PCCC via cip-path workaround (5/5 stages)

Replaced the "ab_server PCCC upstream-broken" skip gate with the actual
root cause: libplctag's ab_server rejects empty CIP routing paths at the
unconnected-send layer before the PCCC dispatcher runs. Real SLC/
MicroLogix/PLC-5 hardware accepts empty paths (no backplane); ab_server
does not. With `/1,0` in place, N (Int16), F (Float32), and L (Int32)
file reads + writes round-trip cleanly across all three compose profiles.

## Fixture changes

- `AbLegacyServerFixture.cs`:
  - Drop `AB_LEGACY_TRUST_WIRE` env var + the reachable-but-untrusted
    skip branch. Fixture now only skips on TCP unreachability.
  - Add `AB_LEGACY_CIP_PATH` env var (default `1,0`) + expose `CipPath`
    property. Set `AB_LEGACY_CIP_PATH=` (empty) against real hardware.
  - Shorter skip messages on the `[AbLegacyFact]` / `[AbLegacyTheory]`
    attributes — one reason: endpoint not reachable.

- `AbLegacyReadSmokeTests.cs`:
  - Device URI built from `sim.CipPath` instead of hardcoded empty path.
  - New `AB_LEGACY_COMPOSE_PROFILE` env var filters the parametric
    theory to the running container's family. Only one container binds
    `:44818` at a time, so cross-family params would otherwise fail.
  - `Slc500_write_then_read_round_trip` skips cleanly when the running
    profile isn't `slc500`.

## E2E + seed + docs

- `scripts/e2e/test-ablegacy.ps1` — drop the `AB_LEGACY_TRUST_WIRE`
  skip gate; synopsis calls out the `/1,0` vs empty cip-path split
  between the Docker fixture and real hardware.
- `scripts/e2e/e2e-config.sample.json` — sample gateway flipped from
  the hardware placeholder (`192.168.1.10`) to the Docker fixture
  (`127.0.0.1/1,0`); comment rewritten.
- `scripts/e2e/README.md` — AB Legacy expected-matrix row goes from
  SKIP to PASS.
- `scripts/smoke/seed-ablegacy-smoke.sql` — default HostAddress points
  at the Docker fixture + header / footer text reflect the new state.
- `tests/.../Docker/README.md` — "Known limitations" section rewritten
  to describe the cip-path gate (not a dispatcher gap); env-var table
  picks up `AB_LEGACY_CIP_PATH` + `AB_LEGACY_COMPOSE_PROFILE`.
- `docs/drivers/AbLegacy-Test-Fixture.md` + `docs/drivers/README.md`
  + `docs/DriverClis.md` — flip status from blocked to functional;
  residual bit-file-write gap (B3:0/5 → 0x803D0000) documented.

## Residual gap

Bit-file writes (`B3:0/5` style) surface `0x803D0000` against
`ab_server --plc=SLC500`; bit reads work. Non-blocking for smoke
coverage — N/F/L round-trip is enough. Real hardware / RSEmulate 500
for bit-write fidelity. Documented in `Docker/README.md` §"Known
limitations" + the `AbLegacy-Test-Fixture.md` follow-ups list.

## Verified

- Full-solution build: 0 errors, 334 pre-existing warnings.
- Integration suite passes per-profile with
  `AB_LEGACY_COMPOSE_PROFILE=<slc500|micrologix|plc5>` + matching
  compose container up.
- All four non-hardware e2e scripts (Modbus / AB CIP / AB Legacy / S7)
  now 5/5 against the respective docker-compose fixtures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/drivers/AbLegacy-Test-Fixture.md

@@ -93,11 +93,13 @@ cover the common ones but uncommon ones (`R` counters, `S` status files,
 
 ## Follow-up candidates
 
-1. **Fix ab_server PCCC coverage upstream** — the scaffold lands the
-   Docker infrastructure; the wire-level round-trip gap is in ab_server
-   itself. Filing a patch to `libplctag/libplctag` to expand PCCC
-   server-side opcode coverage would make the scaffolded smoke tests
-   pass without a golden-box tier.
+1. **Expand ab_server PCCC coverage** — the smoke suite passes today
+   for N (Int16), F (Float32), and L (Int32) files across SLC500 /
+   MicroLogix / PLC-5 modes with the `/1,0` cip-path workaround in
+   place. Known residual gap: bit-file writes (`B3:0/5`) surface
+   `0x803D0000`. Contributing a patch to `libplctag/libplctag` to close
+   this + documenting ab_server's empty-path rejection in its README
+   would remove the last Docker-vs-hardware divergences.
 2. **Rockwell RSEmulate 500 golden-box tier** — Rockwell's real emulator
    for SLC/MicroLogix/PLC-5. Would close UDT-equivalent (integer-file
    indirection), timer/counter decomposition, and real ladder execution
@@ -114,7 +116,8 @@ cover the common ones but uncommon ones (`R` counters, `S` status files,
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs`
   — TCP probe + skip attributes + env-var parsing
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs`
-  — three wire-level smoke tests (currently blocked by ab_server PCCC gap)
+  — wire-level smoke tests; pass against the ab_server Docker fixture
+  with `AB_LEGACY_COMPOSE_PROFILE` set to the running container
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml`
   — compose profiles reusing AB CIP Dockerfile
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md`