Hosted compositions compose without the local group-commit writer

[kfallah]

Platform #620 (merged) composes the native control plane over Postgres-backed components with no write_ledger; at the pinned revision NativeControlPlane.__init__ unconditionally runs SyncGroupCommitLedger(components.write_ledger), so the hosted worker crashes at startup:

AttributeError: 'HostedNativeGatewayComponents' object has no attribute 'write_ledger'

(reproduced against platform main's exact pin before writing this fix.)

Root cause: the hosted seam leaked local-engine implementation details — the components protocol demanded the SQLite group-commit batching writer, which a Postgres host cannot honestly provide.

• write_ledger is now GroupCommitAttemptLedger | None; hosted stores return None or omit the attribute (getattr fallback keeps platform's current dataclass working with just a pin bump)
• ledger is retyped as a structural SyncWriteLedger protocol: the synchronous, thread-safe durable surface data-plane threads settle through; the local composition still batches through the group-commit facade unchanged
• Regression tests construct the control plane over hosted-shaped components (attribute absent, and None) and settle a request end to end through the raw path

After this merges, platform only needs to bump its experiential pin — no platform code changes.

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR allows the native control plane to run over hosted components that lack the local SQLite group-commit writer, falling back to their synchronous durable ledger while preserving local batching.

• Introduces a structural synchronous ledger contract for admission and settlement writes.
• Makes the local group-commit writer optional and supports components that omit the attribute.
• Moves shared quota-error construction into the settlement module.
• Adds regression coverage for hosted-shaped components using both absent and null writers.

Confidence Score: 5/5

The PR appears safe to merge with no concrete blocking or independently actionable non-blocking issue identified.

The hosted fallback matches the bridge’s synchronous write call surface, local compositions retain their existing group-commit path, and regression tests cover both supported forms of a missing writer.

Important Files Changed

Filename	Overview
exp/runtime/gateway/native_bridge.py	Selects either the local group-commit facade or the hosted synchronous ledger and reuses the shared quota-error helper.
exp/runtime/gateway/native_components.py	Defines the synchronous durable write protocol and makes the local group-commit writer optional.
exp/runtime/gateway/native_bridge_test.py	Adds end-to-end regression coverage for hosted-shaped components with an absent or null group-commit writer.
exp/runtime/gateway/native_settlement.py	Centralizes construction of the public monthly-quota protocol error.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[NativeControlPlane initialization] --> B{write_ledger present?}
    B -->|Yes| C[SyncGroupCommitLedger facade]
    B -->|No or None| D[Hosted synchronous ledger]
    C --> E[Accept request and start attempt]
    D --> E
    E --> F[Provider dispatch]
    F --> G[Durable terminal settlement]

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