feat: per-source toggle to back up OneDrive cloud-only placeholder files (#133)

## What & why

Issue #4: give each backup source a policy for OneDrive / cloud-only
placeholder
files. Windows OneDrive Files-On-Demand marks a dehydrated placeholder
with
`FILE_ATTRIBUTE_RECALL_ON_OPEN`; opening it forces a network hydration,
so the
scanner has always skipped these by default (DESIGN s5.2.1) to avoid
silently
pulling down terabytes of cloud-only data. Some users, though, *want*
those files
backed up. This adds a per-source opt-in to do exactly that.

## Policy semantics

New `PlaceholderPolicy` (serde snake_case) carried end-to-end:

- **`skip`** (default): unchanged behaviour - a cloud-only placeholder
is skipped
before stat/hash and its existing `file_state` row is preserved (not
treated as
  a deletion).
- **`force_download`**: the scanner does NOT skip on the recall
attribute; the
file flows through the normal open/read path and Windows hydrates it on
read
(the byte read happens downstream at hash/upload time, so scan-time
`stat`
  never triggers hydration).

Stored as a new **nullable** `placeholder_policy` TEXT column (migration
`0008`).
`NULL` (every pre-migration row) and any unrecognised value decode to
`skip`, so
the change is fully backward compatible with no data migration.

## Shape

- `crates/driven-core`: `PlaceholderPolicy` enum +
`SourceRow.placeholder_policy`,
migration `0008`, 5 sqlx query sites (2 SELECT + 3 upsert) + regenerated
  committed `.sqlx/`. Scanner gates the skip via a pure
  `should_skip_placeholder(attrs, policy)` fn (mirrors the repo's
`classify_*` / `fallback_decision` pure-decision pattern) so both
branches are
unit-testable cross-platform (the real attribute cannot be synthesised
on a
  temp file portably).
- IPC: `AddSourceRequest` (`#[serde(default)]`), `SourcePatch`
(`Option<PlaceholderPolicy>`), and `SourceDto` gain the field; wired
through
  `add_source` / `update_source`. TS mirrors updated in `ipc/types.ts`.
- UI: a "Back up OneDrive cloud-only files" toggle with an explanatory
caption in
BOTH the add-source wizard (exclusions step) and the SourceTable inline
edit
  panel; strings localized in `en-US.json`.

## Tests

- Rust: `should_skip_placeholder` both-policy unit test; `from_db`
NULL/unknown ->
skip + encode round-trip; sqlite `placeholder_policy_round_trip`
(default +
force_download persist/reload/flip). `cargo fmt --check`, `clippy
--workspace
--all-targets -D warnings`, `cargo test -p driven-core / -p driven-app /
-p driven-cli / -p driven-chaos` all green. Migration `0008` verified
applying
  in order.
- UI: extended `settings-components.test.ts` with mount tests exercising
the new
toggle in the wizard and both SourceTable states (reflect current policy
+
patch on save). `pnpm lint`, `vue-tsc --noEmit`, `pnpm test:unit` all
green.

Note: the scanner import of `PlaceholderPolicy` is `#[cfg(any(windows,
test))]`
gated to match its only (cfg-gated) consumer, so the non-Windows CI
clippy legs
stay warning-free.

Refs #34 (backlog item: OneDrive cloud-only placeholders).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: pmaxhogan

.sqlx/query-3195ca7d060e43ce8be8651e66bd65239aaede46a6d237390abeda1a119a2d75.json

@@ -141,6 +141,7 @@ fn source_in(account: AccountId, root: &std::path::Path, folder_id: &str) -> Sou
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,

…2371271105bd7ef3f626cd970a5920bb548.json …4aea61375d50d79cf95105980d318db5ff9.json.sqlx/query-eee4b2498d829e426305b803d63a62371271105bd7ef3f626cd970a5920bb548.json renamed to .sqlx/query-519c2f6c9e040c67a14f44d92553d4aea61375d50d79cf95105980d318db5ff9.json .sqlx/query-eee4b2498d829e426305b803d63a62371271105bd7ef3f626cd970a5920bb548.json renamed to .sqlx/query-519c2f6c9e040c67a14f44d92553d4aea61375d50d79cf95105980d318db5ff9.json

@@ -97,6 +97,7 @@ fn source_in(account: AccountId, root: &std::path::Path, folder_id: &str) -> Sou
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,

…fbd6f7d1e66bdbe62fa84429740ef5cf9ba.json …78c3be90e8863d8eaa89733fd6f20cc5ce8.json.sqlx/query-af709bab951a1b495c05e5f4179a9fbd6f7d1e66bdbe62fa84429740ef5cf9ba.json renamed to .sqlx/query-95c1eb7488ee60abedbc08d67ca4c78c3be90e8863d8eaa89733fd6f20cc5ce8.json .sqlx/query-af709bab951a1b495c05e5f4179a9fbd6f7d1e66bdbe62fa84429740ef5cf9ba.json renamed to .sqlx/query-95c1eb7488ee60abedbc08d67ca4c78c3be90e8863d8eaa89733fd6f20cc5ce8.json

@@ -145,6 +145,7 @@ fn source_in(account: AccountId, root: &Path, folder_id: &str) -> SourceRow {
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,

.sqlx/query-a450f209392b6f773adb766d1ffdbc50647a6b4e1cea4a4b2f92460200031be9.json

@@ -240,6 +240,7 @@ fn source_row(account: driven_core::types::AccountId, root: &Path, folder_id: &s
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,

crates/driven-chaos/src/scenarios/concurrency.rs

@@ -188,6 +188,7 @@ fn source_in(account: driven_core::types::AccountId, root: &Path, folder_id: &st
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,

crates/driven-chaos/src/scenarios/drive_side.rs

@@ -147,6 +147,7 @@ fn flat_source(account: AccountId, root: &Path, folder_id: &str) -> SourceRow {
         respect_gitignore: false,
         include_patterns: vec![],
         exclude_patterns: vec![],
+        placeholder_policy: Default::default(),
         schedule_json_v2_reserved: None,
         deep_verify_interval_secs: 604_800,
         last_full_scan_at: None,