Support provider-owned fresh retry workspaces (#17252)

## Thinking Path

> - Paperclip coordinates AI agents and retains their work across
failures.
> - A retry can require a new workspace while preserving the failed
attempt.
> - Core rejects this recovery strategy for provider-owned storage.
> - Providers should implement the required outcome using their own
storage design.
> - This pull request adds a semantic fresh-preparation contract and
delegates recovery preparation.
> - The benefit is that a supported provider can run a fresh retry
without losing prior work.

## Linked Issues or Issue Description

**What happened?**
A retry that selects `fresh_isolated_workspace` fails with
`fresh_workspace_storage_unsupported` for provider-owned storage.

**Expected behavior**
Core asks a capable provider to prepare new storage and attach verified
recovery files. The failed workspace remains intact.

**Steps to reproduce**
Run a task in a task-capable plugin environment. Let the task fail
without a verified workspace preservation receipt. Retry the task so
Core selects a fresh attempt.

**Paperclip version or commit**
6204239cf (rebased on current master).

**Deployment mode**
Self-hosted server with a plugin task environment and managed workspace
provider.

Search found no duplicate implementation. This branch includes the
default-provider changes from #17247 and preserves their source
selection behavior.

## What Changed

- Define an opt-in fresh-preparation contract with a stable attempt
identity and verified recovery file descriptors.
- Describe retained-storage and recovery-attachment guarantees without
requiring a Git storage layout.
- Reserve replacement task bindings with revision checks and keep the
failed workspace intact. Projectless and project-backed task
environments both replay their stable attempt reservation.
- Reconcile an interrupted preparation against its reserved workspace
and stable operation identity.
- Stage verified recovery archives at stable transfer paths. Delegate
attachment materialization to the provider.
- Preserve projectless attempt directory identities through later turns
and pin the intent into each execution lease.
- Protect fresh intent and projectless ownership from caller metadata
replacement or injection.

## Verification

- SDK workspace-provider tests: 4 passed.
- Targeted reservation and task-dispatch tests: 31 passed.
- Recovery transfer staging and lifecycle focus: 7 passed. The separate
cache-cleanup failure reconciliation case also passed.
- After rebasing on current master, 7 focused preparation and ownership
cases passed. These cover inherited provider defaults, fresh
preparation, stable projectless identity, and authorization denial.
- The focused metadata authority regression passed, including forged
intent, replacement, and null metadata patches.
- Three assembled interrupted task-reservation cases passed:
projectless, project with a saved source, and project with a newly
selected default source.
- Targeted tests use worktree SDK sources. No full local build or
typecheck ran.
- Local checks remain targeted as requested. Latest-head GitHub CI
passed: 54 successful checks, including typecheck, build, server suites,
Runner validation, and E2E shards; 2 unrelated Storybook checks were
skipped.
- Greptile reviewed commit 73595b0c61 at
5/5 with zero unresolved threads.
- Live VM E2E has not run.

## Risks

- Existing providers retain their existing behavior. Fresh attempts
require explicit version support.
- The companion provider implementation must materialize recovery
snapshots safely and preserve the old workspace.
- Fresh retries require the companion provider implementation. Providers
without the version marker fail closed.

## Model Used

- OpenAI GPT-6.1 (`gpt-6.1-sol`), reasoning and coding tools. The
runtime does not expose the context-window limit.

## 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>

packages/shared/src/types/plugin.ts

@@ -193,6 +193,7 @@ export interface SandboxProviderCapabilities {
 export interface PluginEnvironmentDriverDeclaration {
   /** Provides Runner execution, resource preparation, and PRP connections via environmentTask. */
   supportsTasks?: boolean;
+  freshWorkspaceVersion?: 1;
   /** Stable driver key, unique within the plugin. Namespaced by plugin ID at runtime. */
   driverKey: string;
   /**
@@ -696,6 +697,7 @@ export interface PaperclipPluginManifestV1 {
   agentLifecycle?: true;
   /** Own project storage and durable workspace operations as one contract. */
   workspaceProvider?: {
+    freshWorkspaceVersion?: 1;
     modes: Array<"shared_workspace" | "isolated_workspace" | "operator_branch">;
     strategies: Array<"project_primary" | "git_worktree">;
     defaultForProjects?: {

packages/shared/src/validators/plugin.ts

@@ -178,6 +178,7 @@ export type SandboxProviderCapabilitiesInput = z.infer<typeof sandboxProviderCap
 // (for example `supportsLoginPTY`) fails validation instead of dropping.
 export const pluginEnvironmentDriverDeclarationSchema = z.object({
   supportsTasks: z.boolean().optional(),
+  freshWorkspaceVersion: z.literal(1).optional(),
   driverKey: z.string().min(1).regex(
     /^[a-z0-9][a-z0-9._-]*$/,
     "Environment driver key must start with a lowercase alphanumeric and contain only lowercase letters, digits, dots, hyphens, or underscores",
@@ -791,6 +792,7 @@ export const pluginManifestV1Schema = z.object({
   capabilities: z.array(z.enum(PLUGIN_CAPABILITIES)).min(1),
   agentLifecycle: z.literal(true).optional(),
   workspaceProvider: z.object({
+    freshWorkspaceVersion: z.literal(1).optional(),
     modes: z.array(z.enum(["shared_workspace", "isolated_workspace", "operator_branch"])).min(1).max(3),
     strategies: z.array(z.enum(["project_primary", "git_worktree"])).min(1).max(2),
     defaultForProjects: z.object({