Index reads fail with `Not found: .../tree/<parent>/_indices/...` through a branch created from another branch

[ragnorc]

An index created on a dataset is reachable through a first-generation branch (shallow clone) via the clone's base_paths redirect, but a branch created from that branch records its index redirect against the immediate parent tree instead of composing the parent's own redirect to where the index files physically live. Every index-consuming read through the second-generation branch then fails with a Not found on .../tree/<parent>/_indices/....

resolve_base_uri resolves a file's location by looking up its base_id in manifest.base_paths. A shallow clone (Operation::Clone from Dataset::create_branch) populates base_paths with a redirect to the source tree. When the source is itself a clone, the redirect points at the source's tree path (.../tree/<parent>/_indices/...) — but the index files were never copied there; the parent reached them through its own base_paths entry, which the grandchild does not chain to.

Repro (Rust, v9.0.0-beta.21 / rev 1aec1465; both IndexType::BTree and IndexType::Inverted reproduce it):

// dataset + a scalar index on `value`
let mut ds = /* write small dataset */;
ds.create_index_builder(&["value"], IndexType::BTree, &ScalarIndexParams::default())
    .replace(true).await?;

// first-generation branch + a write — indexed reads WORK here
let mut feature = ds.create_branch("feature", ds.version().version, None).await?;
feature.append(/* one batch */, None).await?;
scan_with_filter(&feature, "value = 1").await?;   // ok

// second-generation branch: clone the clone
let experiment = feature
    .create_branch("experiment", feature.version().version, None).await?;

// the same indexed read now fails:
//   Not found: .../tree/feature/_indices/<uuid>/page_lookup.lance
scan_with_filter(&experiment, "value = 1").await;   // Err(NotFound)

BTREE surfaces it as a missing page_lookup.lance, inverted/FTS as a missing tokens.lance. The files exist under the original dataset root's _indices/. A non-indexed scan of the same second-generation branch returns the rows correctly, so this is specifically index-file resolution, not data-file resolution.

Expected: index reads through any depth of shallow-clone lineage resolve to the tree that physically holds the index files — either by composing the transitive base_paths redirect at clone time, or by resolving base_id transitively at read time.

Suggested validation: an indexed dataset, a branch-of-a-branch, and an indexed read through the grandchild that returns the same rows a non-indexed scan does; cover BTREE and inverted indexes, and a third-generation clone.

Related (checked; none is this bug): #4863 "shallow_clone support indexes" (closed) added index support for a single clone level — this repro shows one level works and the second level breaks. #7785 (use original base paths when writing to a branch) and #7515 (in-place materialize of base-referenced files) touch the same base_paths subsystem from the data-file / feature side. #4853 is the shallow_clone→branch epic. This is the index-file correctness face of that cluster and is not tracked by any of them.

[ragnorc]

Additional confirmation that this is not a call-form issue: the failure reproduces identically for both ways of creating the second-generation branch.

• Form A — create_branch on the branch handle: feature.create_branch("experiment", feature_version, None).
• Form B — the cross-source form used by the repo's own test_create_branch_and_shallow_clone_from_other_branch: main_ds.create_branch("experiment", ("feature", feature_version), None).

Both yield Not found: .../tree/feature/_indices/<uuid>/page_lookup.lance on an indexed read through experiment, while a first-generation indexed read (through feature) returns correctly, and a non-indexed scan through experiment returns the right rows. So the branch itself resolves data correctly; only index-file base-path resolution fails to chain through the second clone generation.