P5: busbar-transport-stdio leaves for its own repo, pinned (/status row 158)

[MattJackson]

/status row 158: extract busbar-transport-stdio to its own repo and pin it. Crates go 24 -> 23. Not $.

Spec:

• BUSBAR-1.6.0.md l.2220 (deps: bump jsonschema from 0.49.2 to 0.49.5 #39): "plugin SOURCE never re-enters busbar".
• l.3962: each plugin crate is pinned back as a git dependency in the root manifest's linked rows.

It uses the same pattern as tcp, http, ws and store-memory (#783).

Based on predev, not on #561. The only stdio coupling #561 has is two TransportTail fields in src/meta.rs (fault_rows, fault_rows_len). #778/#787 carry the same hunk. So #561 needs a stdio pin the same way it already pins tcp, ws, http and grpc (p2-breaker-neutral-ts-pin); it no longer needs an in-tree edit. #561 is a conflicting draft, and stacking this on it would hold row 158 behind it.

What

• crates/busbar-transport-stdio is deleted. repin: busbar 5c99befcfa; busbar deletes its in-tree stdio crate and pins this repo (P5, row 158) busbar-transport-stdio#14 (CI green) carries it at busbar pin 5c99befcfa.
  • It is byte for byte, except that lib.rs uses the twin layout: the cdylib export is in transport-stdio-plugin, not behind dropped-in.
  • The root pins its head 604a5caf13 with one git row.
• The root's edge takes the workspace row. Its transport-stdio linked and linked-axes rows are unchanged.
• deny.toml: allow-git gains the repo.
• plugins.yaml: drops pending_crate.
• Cargo.lock: the package resolves from git. busbar-contract stays patched to the path crate.

Selftests

• linked-dropped-features and plugin-closure-deps scan workspace members only. Their plants move from the stdio crate to busbar-transport-webrtc, the one transport still in crates/.
• kind-isolation's plants keep their crates/busbar-transport-stdio paths. The gate lays every pinned plugin-kind checkout at crates/<package> beneath its overlay (kind_isolation/pinned.rs), as it does for tcp, http and ws.

Ledgers

• Removed: qa/construction.toml's manifest-allowlist row for stdio. It already named deps the manifest no longer had, and the ws extraction removed its row the same way.
• Unchanged: the census floor transport = 1 (webrtc still matches it).
• Kept, because each is still measured from the pinned checkout:
  • kind-isolation's stdio×plane cell and its busbar -> busbar-transport-stdio edge. The mount reads the crate as it read it in-tree; busbar-store-memory keeps the same rows after P5: extract store-memory to GetBusbar/busbar-store-memory (pinned); plugin-ci builds the release image the conformance suite loads #783.
  • the dep-wall carrier exemption (the crate still resolves).
  • the audit-ledger scopes (audit-ledger: pinned plugin scopes read from the pinned checkout #589 reads pinned scopes from the checkout).
• No ceiling moves, because no measured code leaves a gate's view.

Conflicts (merge-tree against open PRs)

• breaker: no protocol in kernel; the transport states its fault table, PIECE_END=128 rides the same framer lineage (row 66) #561 (draft): Cargo.toml, Cargo.lock and a modify/delete on crates/busbar-transport-stdio/src/meta.rs. Its stdio hunk becomes a pin bump to a p2-breaker-neutral-ts-pin branch of the stdio repo.
• P3 FLIP-A2A: the a2a plane served through its door; busbar-a2a deleted (stacked on #778) #787 (a2a flip, stacked on row 68: the breaker reads a plane fault at the far end (stacked on #561) #778): a modify/delete on the same meta.rs, with the same fix.
• Clean against P5 row 106/107: extract busbar-plane-mcp to GetBusbar/busbar-plane-mcp (pinned); every gate reads the pinned planes as its base layer #838, P5: busbar-plane-decisions leaves for its own repo, pinned (/status rows 106/107; stacked on #838) #888, plane-delete-test: a pinned plane is deleted by its pin and feature (stacked on #888) #894, FLIP-STREAMING: the streaming plane served through its door; busbar-voice deleted #503, row 159: a settings-derived need target drops its userinfo; the webhook sink sends it as Basic, as 1.5.5 did (audit export-webhook #1, HIGH) #842 and row 163: retire busbar-release from busbar — docs and comments name ModernCI, not the hop/turnstile/EC2 fleet #830.