fix(core): replay cached CUA back/forward navigation steps

[BABTUNA]

why

CUA replay currently records back/forward steps but AgentCache only
replays navback.
This causes cached CUA runs to silently skip history navigation actions,
which can drift page state and break deterministic replay.

what changed

• Added explicit replay step types for:
  • back
  • forward
• Updated AgentCache replay switch to execute:
  • back via page.goBack(...)
  • forward via page.goForward(...)
• Kept existing navback replay behavior for compatibility.
• Extended unit tests to verify replay of non-act navigation steps:
  • goto
  • navback
  • back
  • forward

test plan

• prettier --check on touched files
• eslint on touched files
• tsc -p packages/core/tsconfig.json --noEmit
• Unit test coverage added in:
  • packages/core/tests/unit/cache-llm-resolution.test.ts

---

Summary by cubic

Fixes cached CUA replays skipping browser history. AgentCache now replays back and forward steps to keep page state deterministic.

• Bug Fixes
  • Added back and forward replay step types and handle them in AgentCache via page.goBack/page.goForward with waitUntil (default domcontentloaded).
  • Preserved existing navback behavior for compatibility.
  • Extended unit tests to cover goto, navback, back, and forward.

^{Written for commit c3362fc. Summary will update on new commits. Review in cubic}

[changeset-bot]

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Latest commit: c3362fc

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[github-actions]

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Approving the latest commit mirrors it into an internal PR owned by the approver.
If new commits are pushed later, the internal PR stays open but is marked stale until someone approves the latest external commit and refreshes it.

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

Architecture diagram

sequenceDiagram
    participant Runner as Replay Runner
    participant Cache as AgentCache
    participant Ctx as V3Context
    participant Page as Browser Page

    Note over Runner,Page: Replay of Cached Agent Steps

    Runner->>Cache: executeCachedSteps(entry)
    loop For each Step in entry.steps
        
        alt Step: goto
            Cache->>Ctx: awaitActivePage()
            Ctx-->>Cache: page
            Cache->>Page: goto(url, { waitUntil })
        
        else Step: navback (Legacy)
            Cache->>Ctx: awaitActivePage()
            Ctx-->>Cache: page
            Cache->>Page: goBack({ waitUntil })
        
        else NEW: Step: back
            Cache->>Cache: replayAgentBackStep()
            Cache->>Ctx: awaitActivePage()
            Ctx-->>Cache: page
            Cache->>Page: NEW: goBack({ waitUntil })
            Page-->>Cache: navigation complete
        
        else NEW: Step: forward
            Cache->>Cache: replayAgentForwardStep()
            Cache->>Ctx: awaitActivePage()
            Ctx-->>Cache: page
            Cache->>Page: NEW: goForward({ waitUntil })
            Page-->>Cache: navigation complete

        else Other steps (act, keys, etc.)
            Cache->>Cache: process step...
        end

    end
    Cache-->>Runner: result (success/failure)

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