#35581 node: add block template manager and track waitNext fee inflow

Consolidates block template creation, waiting, and submission helpers into a `BlockTemplateManager` class registered with validation signals. Adds a `MempoolUpdated` validation interface event that tracks before-and-after fee rate diagram chunks with transaction references. Leverages these diagram snapshots to monitor mempool fee inflow per active template, replacing the polling loop in `waitNext` that assembled full blocks on each tick.

Problem: To check whether newly arriving transactions justify issuing a fresh block template, `waitNext` in the IPC mining interface repeatedly acquires `cs_main` and builds complete block templates solely to sum and compare their fees. Additionally, mining utility functions are free functions scattered across `miner.cpp` requiring manual threading of dependencies, and `SubmitBlock` allocates a throwaway validation listener on every block submitted.

Evidence of importance:

• PR description: 'Currently, to decide whether mempool fee inflow rose enough to be worth a new template, waitNext locks cs_main and assembles a full block template every tick just to sum its fees and compare. After cluster mempool... we shouldn\'t have to build a whole block template to answer that question.'
• PR description links to Delving Bitcoin research: 'determining-blocktemplate-fee-increase-using-fee-rate-diagram/2052'.
• Author notes the fuzz harness for the new manager uncovered a miner chunk-limit check bug fixed in merged PR #35580.

Scope: About half of the patch (+1090 lines) consists of tests, including a new fuzz harness for `BlockTemplateManager` and unit tests in `mempool_update_tests.cpp`. The manager refactor was originally split into #35675 (now merged), and this branch retains the commits up through fee-inflow tracking.

Risk of a mistake: medium (mempool_policy, validation, tests). Mistakes in mempool chunk fee tracking or validation signal ordering could cause mining clients to stall, miss profitable transactions, or encounter deadlocks.

Changed since the previous assessment: The prior dependency #35675 was merged upstream; this branch remains to be rebased on top of it.

Ready · Needs rebase

Conflicts with master; review the logic now, the rebase is mechanical.

Waiting on (from the thread read):

• author: address comments and update PR after opening the standalone BlockTemplateManager PR #35675 2026-07-01
• author: address comments and extract BlockTemplateManager into dedicated PR 2026-07-01

Strong

substantive support, no open objection (pablomartin4btc)

Thread notes: Reclassified Sjors' and pablomartin4btc's review comments as suggestions since neither stated a concrete harm of merging as-is. Added missing suggestion rc:3506167320. / Reclassified Sjors's PR split request and pablomartin4btc's precondition doc request from objections to suggestions under the current rules, since neither names a concrete cost of merging as-is. Added pablomartin4btc's suggestion on restoring the miner comment.

Objections, suggestions, and questions:

Support:

• w0xlt (contributor) (Concept ACK, 2026-06-22): (no reason given) [not substantive]
• pablomartin4btc (member) (Concept ACK, 2026-07-01) [read: src/node/block_template_manager.cpp]: The approach of moving free functions onto a class that holds state plus incremental snapshot tracking to avoid full template rebuilds seems clean. The fuzz test catching an actual bug (#35580) is a strong signal.

Participants:

• w0xlt (contributor, support, 1 statements 2026-06-22 to 2026-06-22): Concept ACK
• Sjors (member, neutral, 1 statements 2026-06-25 to 2026-06-25): suggested splitting BlockTemplateManager into its own PR
• pablomartin4btc (member, support, 3 statements 2026-07-01 to 2026-07-01): Concept ACK; suggested documenting a precondition and restoring an updated comment

1474 lines under test/bench/ci.

• src/test/fuzz/block_template_manager.cpp +556/-0
• src/test/mempool_update_tests.cpp +535/-0
• src/node/block_template_manager.cpp +245/-46
• src/test/miner_tests.cpp +259/-29
• src/txmempool.cpp +149/-41
• src/node/block_template_manager.h +139/-10
• src/txgraph.cpp +47/-17
• src/test/fuzz/txgraph.cpp +23/-12
• src/node/interfaces.cpp +24/-4
• src/txgraph.h +21/-4
• src/validationinterface.cpp +24/-0
• src/test/util/setup_common.cpp +19/-0
• src/util/hasher.cpp +19/-0
• src/kernel/mempool_entry.h +18/-0
• src/node/miner.h +15/-3
• src/policy/packages.cpp +4/-14
• src/test/blockencodings_tests.cpp +9/-4
• src/txmempool.h +9/-2
• src/policy/fees/mempool_estimator.cpp +8/-2
• src/node/miner.cpp +8/-1
• src/validationinterface.h +9/-0
• src/init.cpp +7/-0
• src/util/hasher.h +4/-0
• test/functional/interface_zmq.py +2/-2
• src/test/fuzz/tx_pool.cpp +1/-2
• src/bench/mempool_stress.cpp +1/-1
• src/test/fuzz/connect_block.cpp +1/-1
• src/test/fuzz/utxo_snapshot.cpp +1/-1
• src/test/mempool_tests.cpp +1/-1
• src/test/rbf_tests.cpp +1/-1
• src/test/util/setup_common.h +2/-0
• src/test/util/validation.cpp +1/-1
• src/test/validation_chainstatemanager_tests.cpp +1/-1
• src/validation.cpp +1/-1
• src/wallet/test/fuzz/fees.cpp +1/-1
• src/node/mining_types.h +1/-0
• src/test/CMakeLists.txt +1/-0
• src/test/fuzz/CMakeLists.txt +1/-0
• src/test/fuzz/package_eval.cpp +0/-1

The short text the ranking pass compares across PRs.

Introduces a BlockTemplateManager and adds a MempoolUpdated validation interface signal carrying fee rate diagram chunk changes. Currently, waitNext repeatedly acquires cs_main and constructs full block templates every tick solely to determine if fee increases justify a new template. By tracking fee-rate diagram deltas across mempool updates, waitNext detects staleness without redundant block assembly. Mining helper functions and block submission are also centralized into the manager.

P3 · new feature

Adds incremental feerate diagram snapshot diffing to `txmempool` and `txgraph` when transactions enter or leave the pool. While driven by mining needs, it introduces a useful notification mechanism for pool state changes without altering core policy or acceptance rules.

Membership: Modifies txmempool and txgraph to compute and emit before-and-after fee rate diagram chunks upon mempool updates.

Factors: security/stability 1, bug 0, performance 2, user value 1, leverage 1

P2 · speedup (ranking pass: Root of the BlockTemplateManager chain (#33922, #36356, #36357 build on it) as well as a measurable CPU/lock-contention win for template polling.)

Replaces the polling loop in `waitNext` that assembled complete block templates and acquired `cs_main` on every tick with incremental fee-rate diagram tracking. This avoids significant CPU overhead and lock contention for miners waiting on template updates.

Membership: Carries the Mining label and redesigns block template creation, waitNext, and fee inflow tracking under BlockTemplateManager.

Factors: security/stability 1, bug 0, performance 2, user value 1, leverage 1