serviceability-instruction: topology + feed builders (RFC-26 R7)

[juan-malbeclabs]

Summary

RFC-26 R7 (stacked on the previous phase's branch). Topology create/delete plus batched clear_topology / assign_topology_node_segments (single-chunk + *_batched; CLEAR_BATCH_SIZE=16 / BACKFILL_BATCH_SIZE=4 moved into the crate). Feed create/update/delete.

All builders route through authorize() -> build_with_permission unless noted; each carries a verbatim account-layout doc-comment copied from its processor.

Testing Verification

• Unit tests assert the exact AccountMeta list (incl. trailing [payer, system]) and the borsh tag byte for every builder, covering the conditional/variable-account paths.

Closes #4022. Part of RFC-26 (rfcs/rfc26-rust-instruction-builder-library.md).

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PR stack (RFC-26 builder library)

Stacked PRs, merge in order (each is based on the previous one's branch):

1. serviceability-instruction: scaffold pure instruction-builder crate (RFC-26 R0) #4049 — R0 scaffold + exemplars
2. serviceability-instruction: device domain builders (RFC-26 R1) #4050 — R1 device
3. serviceability-instruction: link domain builders (RFC-26 R2) #4051 — R2 link
4. serviceability-instruction: user domain builders (RFC-26 R3) #4052 — R3 user
5. serviceability-instruction: location/exchange/contributor builders (RFC-26 R4) #4053 — R4 location/exchange/contributor
6. serviceability-instruction: multicastgroup + allowlist builders (RFC-26 R5) #4054 — R5 multicastgroup + allowlists
7. serviceability-instruction: tenant + permission builders (RFC-26 R6) #4055 — R6 tenant + permission
8. serviceability-instruction: topology + feed builders (RFC-26 R7) #4056 — R7 topology + feed ← this PR
9. serviceability-instruction: accesspass + resource builders (RFC-26 R8) #4057 — R8 accesspass + resource
10. serviceability-instruction: globalstate/globalconfig/allowlist/index/migrate builders (RFC-26 R9) #4058 — R9 globalstate/config/allowlist/index/migrate

R10 (commands/* migration + program-test) and RF (fixtures) follow as separate PRs.

[ben-dz]

The topology module doc's name-canonicalization rationale is factually wrong: get_topology_pda (pda.rs:121-124) has uppercased internally since c60e14d, so delete/clear/assign deriving "from the raw arg" still canonicalize and a non-uppercase name can never reference a non-existent account or revert — the builders' to_ascii_uppercase() is a PDA no-op whose only effect is packing the canonical name (itself a byte-parity divergence from the SDK for non-canonical input). Either drop the canonicalization or rewrite the rationale, and fix the test comments repeating the claim. Separately, the live SDK ClearTopologyCommand readonly bug this PR correctly documents is user-facing (clearing a live topology is the mandatory precursor to delete) and has no tracking issue. Builder account layouts, writability flags, wire tags, batch math, and the FEED_AUTHORITY/AUTHORIZE_GATED_FLAGS gap claim all verified correct; remaining items are low-severity doc and test-fixture fixes.

• Medium: the live SDK bug this PR documents at topology.rs:101 ("the SDK command is the one that needs fixing") is real, user-facing, and untracked. smartcontract/sdk/rs/src/commands/topology/clear.rs passes the topology PDA new_readonly, while the processor (clear.rs:124-127) asserts is_writable whenever the topology exists and at least one link is cleared; since delete_topology requires reference_count == 0 (delete.rs:77), clearing a live topology is the mandatory precursor to delete — the SDK/CLI topology clear reverts in exactly its primary use case. No GitHub issue tracks it. File a tracking issue, or fix the one-line new_readonly → new in a small follow-up, so this doc's pointer doesn't dangle indefinitely.

[ben-dz]

lgtm — all findings from previous rounds verified fixed on the current head (canonicalization removed, SDK clear_topology bug tracked in #4078, batch-limit docs corrected, FEED_AUTHORITY gap tracked in #4079 with a passing canary test, realistic FeedUpdateArgs fixture).