feat(duplex): run the Daytona sandbox callback bridge over Node HTTP/2 (#12120)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - Sandbox providers carry agent work through controlled execution
channels
> - The Daytona callback bridge uses a bespoke line-framed protocol over
its duplex channel
> - The bespoke protocol adds framing work and does not use the Node
transport that already supports multiplexed streams
> - This pull request carries raw bytes across the channel, adds a Node
HTTP/2 bridge, and selects it for Daytona
> - The benefit is one authenticated, multiplexed callback session with
queue_v1 as the bounded fallback

## Linked Issues or Issue Description

**Subsystem affected**

The packages/plugins Daytona provider and the shared duplex execution
path.

**Problem or motivation**

The Daytona callback bridge uses a bespoke line-framed protocol over the
provider duplex channel. This adds protocol work and limits stream
handling.

**Proposed solution**

Carry raw bytes through the cross-layer channel. Add an authenticated
Node HTTP/2 host server and sandbox client gateway. Select http2_v1 for
Daytona and retain queue_v1 as the fallback.

**Alternatives considered**

Keep the current duplex_v1 protocol. This keeps the bespoke framing path
and does not provide one HTTP/2 session for callback streams.

**Roadmap alignment**

ROADMAP.md lists Daytona under cloud and sandbox agents. This change
improves the shipped Daytona provider path.

**Additional context**

The branch adds no dependency. Node 24 provides the http2 module. The
host token check and canonical path parser remain the single dispatch
path.

## What Changed

- Carry raw Uint8Array chunks through the adapter, plugin, worker,
runtime, and Daytona layers.
- Encode bytes as base64 only across the JSON-RPC hop, because JSON has
no binary type.
- Add the bounded host HTTP/2 server and the in-sandbox HTTP/2 client
gateway.
- Authenticate every stream with the per-run bridge token before route
work.
- Parse the path once and reuse the canonical result for route and
forwarding work.
- Select http2_v1 for Daytona and fall back once to queue_v1 when the
client preface is absent.
- Add transport, session, stream, and fallback telemetry.
- Mark HTTP/2 as the preferred transport and queue_v1 as the
soft-deprecated fallback.

## Verification

- `npx vitest run packages/adapter-utils/src` — 990 passed and 4
skipped.
- `npx vitest run
server/src/__tests__/plugin-worker-manager-duplex.test.ts` — 32 passed.
- `npx vitest run --config
packages/plugins/sandbox-providers/daytona/vitest.config.ts` — 220
passed and 6 skipped.
- `npx tsc --noEmit` in `packages/adapter-utils`, `packages/shared`,
`packages/plugins/sdk`, and `server` — clean.
- No `package.json` or `pnpm-lock.yaml` file changed.
- The live Daytona test skips when `DAYTONA_API_KEY` is absent.
- The root `npx tsc --noEmit` command has a pre-existing missing
`packages/adapters/droid-local` reference on this branch and on
`master`.

## Risks

- The transport change affects several duplex layers and could expose
byte-boundary errors.
- A missing HTTP/2 client preface falls back once to queue_v1 and
records `preface_missing`.
- The host token check and canonical path parser must remain on the
shared dispatch path.
- The live Daytona test needs `DAYTONA_API_KEY` and does not run in this
agent sandbox.

## Model Used

OpenAI GPT-5, tool-enabled coding agent with repository inspection,
GitHub CLI, and shell execution.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

doc/observability.md

@@ -419,9 +419,9 @@ key never reaches a sink by accident.
 | Key | Type | Optional | Value set |
 | --- | --- | --- | --- |
 | `provider` | string | no | `daytona`, or `other` for any other plugin key. |
-| `transport` | string | no | `duplex` or `file`. A fallback record uses `file`; every other record uses `duplex`. |
+| `transport` | string | no | `duplex`, `http2`, or `file`. `duplex` names the retired bespoke frame protocol; `http2` names the Node HTTP/2 session over the sandbox channel; a fallback record uses `file`. |
 | `outcome` | string | yes | `ok` or `error`. |
-| `fallback_reason` | string | yes | `gate_off`, `capability_absent`, `open_failed`, `ready_invalid`, `ready_nonce_mismatch`, `ready_timeout`, or `contaminated`. It rides only a fallback record. |
+| `fallback_reason` | string | yes | `gate_off`, `capability_absent`, `route_busy`, `entrypoint_sync_failed`, `broker_construction_failed`, `channel_open_failed`, `ready_invalid`, `ready_nonce_mismatch`, `ready_timeout`, `contaminated`, `aggregate_bytes_exceeded`, or `preface_missing`. It rides only a fallback record. `route_busy` marks the process-scoped route ceiling full. `entrypoint_sync_failed` and `broker_construction_failed` mark the named build step. `channel_open_failed` marks a failed channel open. `aggregate_bytes_exceeded` marks a readiness handshake, or an `http2` post-preface pre-bind buffer, where the host fell back because the process aggregate byte ceiling had no room. `preface_missing` marks a missing or an invalid HTTP/2 client connection preface inside the bounded readiness buffer: the host found no valid preface after the accepted READY line, aborted the `http2` open, and moved the run to the file bridge (`queue_v1`) one time. |
 | `loss_class` | string | yes | `pre_dispatch` or `post_dispatch`, relative to the first request dispatch. It rides only a loss record. |
 | `loss_reason` | string | yes | `stdin_eof`, `provider_exit`, `heartbeat_timeout`, `rpc_failure`, `write_error`, `transport_closed`, or `other`. The host maps every loss cause to one of these values, so no raw provider text reaches a sink. `write_error` marks a rejected host-to-sandbox write. `transport_closed` marks a reason-less provider transport close with no exit data. It rides only a loss record. |