[IsolationSession] Refactor runner into per-responsibility module files

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Summary

Splits the 2,860-line src/wxc_common/src/isolation_session_runner.rs
into 9 per-responsibility module files under
src/wxc_common/src/isolation_session/:

Module	Responsibility
mod.rs	Re-exports IsolationSessionRunner (the only externally-reachable type)
error.rs	IsolationSessionError enum + ScriptResponse/MxcError conversions
policy.rs	Phase-specific policy validation + IsolationSessionUser shape check
process_options.rs	ProcessOptions + WinRT IsoSessionProcessOptions translator
folder_sharing.rs	ShareFolderBatchAsync request build + per-path outcome aggregation
protected_paths_filter.rs	Emergency mitigation for MXC issue #330
manager.rs	IsolationSessionManager lifecycle wrapper (1:1 with IsoSessionOps)
one_shot.rs	ScriptRunner impl (full lifecycle in a single process)
state_aware.rs	StatefulSandboxBackend impl (per-phase lifecycle methods)

No external API change: wxc_common::isolation_session::IsolationSessionRunner
remains the only externally-reachable item; every internal symbol is now
pub(super) / module-private.

Notable mechanical changes

• IsolationSessionManager::create_process now returns i32 rather than
  ProcessResult { exit_code, stdout, stderr }. The string fields were
  always empty (output is streamed via relay threads), so this is a pure
  cosmetic simplification — ProcessResult is dropped entirely.
• The STILL_ACTIVE shutdown ladder is extracted into a documented
  wait_with_graceful_shutdown helper. The original error-handling
  contract is preserved: first ExitCode() query is ?-propagated;
  per-tier subsequent queries fall back to STILL_ACTIVE.

Tests

All 81 existing unit tests are preserved, grouped with the code they
cover. Two new pinning tests added in state_aware.rs:
backend_key_matches_wire_format and id_prefix_matches_wire_format.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

Refactors the Windows IsolationSessionRunner backend in wxc_common by splitting the former monolithic isolation_session_runner.rs into a focused module tree under src/wxc_common/src/isolation_session/, while updating call sites to the new module path.

Changes:

• Replaced the single-file IsolationSession runner implementation with a multi-module layout (error, policy, manager, one_shot, state_aware, etc.) under wxc_common::isolation_session.
• Updated executor/dispatcher imports to reference wxc_common::isolation_session::IsolationSessionRunner.
• Preserved and regrouped unit tests alongside the new modules; added pinning tests for state-aware wire-format constants.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/wxc/src/main.rs	Updates the IsolationSession runner import to the new module path.
src/wxc_common/src/state_aware_dispatch.rs	Updates state-aware backend construction to use the new module path.
src/wxc_common/src/lib.rs	Switches exported module from isolation_session_runner to isolation_session.
src/wxc_common/src/isolation_session/mod.rs	Introduces the new IsolationSession module root and defines IsolationSessionRunner.
src/wxc_common/src/isolation_session/error.rs	Moves typed error model + conversions into a dedicated module.
src/wxc_common/src/isolation_session/policy.rs	Moves phase-specific policy validation and user-bundle validation.
src/wxc_common/src/isolation_session/process_options.rs	Moves process option construction and WinRT translation helpers.
src/wxc_common/src/isolation_session/folder_sharing.rs	Moves ShareFolderBatch request building and per-path outcome aggregation.
src/wxc_common/src/isolation_session/protected_paths_filter.rs	Moves the MXC #330 protected-path filter/normalization and tests.
src/wxc_common/src/isolation_session/manager.rs	Moves the IsoSessionOps lifecycle wrapper and process execution/relay logic.
src/wxc_common/src/isolation_session/one_shot.rs	Moves the one-shot ScriptRunner implementation.
src/wxc_common/src/isolation_session/state_aware.rs	Moves the StatefulSandboxBackend implementation and adds wire-format pinning tests.
src/wxc_common/src/isolation_session_runner.rs	Deletes the old monolithic implementation file.