[Frontier] [BROW16-01A] Prove a modern browser mediation contract #408

Parent

#397 — #397; complete S16 target #392.

Model tier

Frontier: this slice requires judgment about protected authority, lifecycle/recovery or a new cross-client/service contract; exact new APIs and migrations are not yet settled.

Context to read

AGENTS.md; CONTEXT.md; docs/agents/workflow.md; docs/specs/S16-rakazo-experience.md; docs/specs/S15-conversational-autonomy.md; ADR 0064 and ADRs 0074–0077; docs/design/S16-rakazo-experience.md; docs/design/S16-mobbin-research.md. Reuse the completed design research; do not repeat broad Mobbin discovery.

Starting implementation/contract surfaces: src/s15/browser/{types,engine,gateway,egress,provisioned}.ts; src/s15/vm/network.ts; docs/contracts/s15-protected-browser-v1.md; docs/contracts/s15-runtime-feasibility-v1.md. Read their current definitions and relevant tests before selecting changes. Paths with braces denote existing module families, not settled new signatures.

Deliverable

Select and demonstrate a useful protected modern-browser architecture with request-level effect/disclosure enforcement and a concrete public Schway/Jit contract. This feasibility child does not close #397.

Baseline and readiness

Audited stack head 17b814220371cd1e2126be2ec9bd9753537f69e6; main remains the pre-S16 baseline. #398/#399/#403/#404 are open drafts, not merged/live acceptance. Existing S15 services are reusable baseline, and #400/#401 supply draft text/binary custody. No new behavior is claimed here. Branches/PRs and issue ownership were inspected on 2026-11-05; this new ticket has no implementation claim. Recheck at dispatch. Preserve the primary-owned jit/402-s16-file-memory branch.

Scoped investigation is eligible after ownership check on this baseline; its output must be reviewed before dependent runtime implementation.

Implementation steps

1. Recheck ownership, branches/PRs, prerequisites and exact source baseline. Compare existing implementation, pinned Rakazo reuse and a simpler alternative; record the chosen tradeoff and versioned contract before coding.
2. Compare existing protected Chromium general mode against a simpler mediated browser service; inspect actual supported public engine contracts.
3. Prototype a real scripted dynamic site with navigation, form editing, JS requests and login handoff outside guest root.
4. Trace fetch/XHR/forms/WebSocket/service-worker/download/redirect and raw protocol/guest egress bypasses; classify supported operations by trusted handlers.
5. Record reviewed request/response/input/credential/settlement contracts, limitations and replacement proof plan in an ADR; publish upstream blocker only for reproduced missing public capability.
6. Integrate the authored experience using real service facts, English/Thai dictionary keys in their designated files, accessible loading/error/empty/reconnect states and current capabilities. For non-UI evidence work, verify those states instead of inventing new UI. Record migrations, compatibility and exact build evidence.

Acceptance criteria

• Dynamic task completes with real browser interaction; static GET alone fails.
• Held exact effect dispatches once and changed payload/recipient invalidates approval.
• Guest root/raw CDP cannot retrieve sessions or bypass mediator.
• Crash after dispatch remains unknown until evidence reconciliation.
• Deliverable works end to end through its actual owning service/client; source presence, transport success and model prose alone are insufficient.
• No S14 default, S15 opt-in, installed policy, historical private scope or owner-host configuration changes without its separate explicit transition.
• New contracts, unresolved limits and exact revision/evidence are recorded; applicable upstream licenses, immutable provenance and modified-file notices ship.

Tests and evidence

1. Dynamic task completes with real browser interaction; static GET alone fails. Use scripted models, protocol fixtures, fake clocks and barriers for deterministic cases; assert actual resulting state/bytes/effects.
2. Held exact effect dispatches once and changed payload/recipient invalidates approval. Use scripted models, protocol fixtures, fake clocks and barriers for deterministic cases; assert actual resulting state/bytes/effects.
3. Guest root/raw CDP cannot retrieve sessions or bypass mediator. Use scripted models, protocol fixtures, fake clocks and barriers for deterministic cases; assert actual resulting state/bytes/effects.
4. Crash after dispatch remains unknown until evidence reconciliation. Use scripted models, protocol fixtures, fake clocks and barriers for deterministic cases; assert actual resulting state/bytes/effects.
5. Run relevant existing module/composed regressions plus the new scenario suite; for rendered behavior, exercise the real bundle in English/Thai, keyboard and mobile widths. Record exact test paths/commands in the PR after implementation selects them.
6. Keep real host/account/device checks opt-in and evidence-labelled; no absent credential blocks independent deterministic work. Public evidence contains hashes/outcomes only; installation-specific details belong in ignored .local records.

Requirements

S16-AC06, S16-AC07; FR-07, FR-10, FR-17, FR-18, FR-35, FR-36, FR-37, FR-38, FR-40, FR-41, NFR-07, NFR-10, NFR-11, NFR-14. Retain S15 authority decisions and FR/NFR identifiers.

Blocked by

None for this bounded feasibility investigation against the pinned planning baseline. It delivers a reviewed contract, not general-browser product acceptance.

Contracts used/delivered

Use current owning POLICY, DATA15, TEAM, MEM, WORK, CHAT and S16 client/file contracts where relevant, plus Schway's supported public host surface. Specific inputs and proposed delivery: src/s15/browser/{types,engine,gateway,egress,provisioned}.ts; src/s15/vm/network.ts; docs/contracts/s15-protected-browser-v1.md; docs/contracts/s15-runtime-feasibility-v1.md. The Deliverable and ordered steps define the missing contract outcome; freeze version, schemas, migration/recovery and conformance fixtures in the implementation ADR/PR. Proposed operations are not already supported APIs. A demonstrated missing engine seam requires a bounded public-only reproduction and a linked Schway contract ticket, never an internal import or duplicate runtime.

Out of scope

Other tickets' outcomes, hosted multi-user SaaS, marketplace operation, upstream branding, silent billing, replacing Schway, general historical data conversion, and unapproved live deployment. Live credentials, real-device acceptance and owner-host cutover are separately owned by LIVE16-01/CUT16-01; deterministic implementation remains in scope.

Do not

Do not use source/model/tool output as authority; expose credentials, sensitive-site sessions or protected state to working execution (trusted-site sessions are the S16-D09 exception); remove guards before proof; auto-retry unknown effects; weaken or bypass the S16-D07 human-required list or let anything but the in-chat owner decision approve it; treat current stack limitations as scope cuts; add model attribution; use implement-parallel; alter #402 ownership; self-merge or deploy. No placeholder controls or fabricated success.

Definition of done

Run bun install --frozen-lockfile, bun run typecheck, bun test --timeout 30000 for affected deterministic suites, and git diff --check; record exact selected suite commands and results. Add real-browser tests for rendered paths and package checks for shipped artifacts. Pure feasibility documentation runs link/coverage checks and git diff --check; a prototype must run its conformance cases. PR body includes Closes #408 and Refs #392, contract versions, tested head and honest pending evidence. No self-merge; parent #392 remains open until full accepted outcomes.

Owner revision 2026-11-06

Grok-style autonomy (S16-D06–D11, ADR 0084) and Telegram removal (ADR 0085) apply. Only the S16-D07 human-required list waits for the owner, approved by a one-press in-chat card; GitHub push/PR/review replies/merge after required checks are the product default; trusted sites may keep sessions in the working VM browser while sensitive sites stay in the protected browser. Jit has no messaging channel; notifications use Web Push (#441). Policy/approval changes belong to #442.

Scope narrowed: the remaining isolation and dispatch-crash proofs apply to the protected browser used for sensitive sites. Public and trusted-site work runs in the working VM browser; record that path and its accepted residual instead of mediating it.