[elpidioassinaturas]

Summary

cube.trend reads a time series from four kinds of cube: a stack of layers, a raster's bands, a Zarr variable, and a STAC collection's band read in place. For a Zarr variable, zarr.reduce (#556) also gives one statistic over time. The other three cubes have nothing like it, so an annual mean NDVI from 16-day composites in the Brazil Data Cube can't be made in RustGIS.

This PR adds cube.reduce. It makes rasters of one statistic of each cell over the dates of any cube cube.trend takes.

• Statistics: mean, min, max, sum, std (the population standard deviation, as in zarr.reduce), count of values, and countAbove a threshold ("above").
• Groups: "by": "all" (the default) makes one layer for the whole period. "year" makes one layer per calendar year, and "month" one per month of the year across the years (a climatology). "start", "end" and "months" pick dates as for a trend.
• Missing values: no-data is skipped cell by cell. "minValid" is the share of a group's dates a cell needs, 0 by default; for example, 0.5 needs half of a year's composites. With the default, count and countAbove give 0 where a cell never had a value.
• Which cubes: two dates or more, from a stack or a raster's bands alike, and a Zarr axis in any order. cube_from now takes what the run needs (TREND or SUMMARY), so cube.trend keeps its own limits: four dates or more, and a Zarr axis in increasing order without repeats. The messages, the web app's included, say "trend" or "summary" as the caller is. A date that can't be read is refused rather than put in a group of its own.
• Size: the slices are folded into running totals as they are read, so a 25-year series takes no more memory than one year. A group's totals are made at its first date and turned into its output at its last, so a summary by year read one date at a time holds one year's totals at a time. A STAC area is read in pieces and stitched as for a trend. The outputs are capped at MAX_VALUES / 2 (32 million values, 8 million in the web app), checked before reading when the cube knows its size and as the pieces are read when it doesn't, with an error that says what to shrink.
• Outputs: the layers are named after what they hold (NDVI mean 2001, NDVI mean 2001–2025 month 03, or the "name" given plus the group), with the period from its earliest date to its latest, and kept in the project as GeoTIFFs, as zarr.reduce does.

Shared with the trend:

• The slice reader, the grid check and the stitching of pieces move out of TrendRun into shared helpers: read_slices, off_grid and Stitch. A trend and a summary therefore read a cube the same way.
• zarr.reduce now uses cube::Stat and its running totals. Its parameters and results are unchanged, and the test checks it value for value against cube.reduce on the same store.
• All of cube.reduce's keys are at the top level of its description, so none is reported as ignored (the issue Analysis: a STAC trend's keys read from cube.trend's description, so none is said to be ignored (#579) #766 fixed for cube.trend).
• Plugins: like cube.trend and zarr.reduce, cube.reduce is in DATABASES, so a plugin needs both the files and network permissions to run it. It is also in DEFAULTS_TO_ACTIVE_LAYER, so a recorded step names the layer it acted on.

Choices in this PR

• No dialog yet; it runs where it is called. The command runs from the CLI, Python, scripts and the MCP server, as cube.trend first did. The app's command search calls it with no parameters, which is refused at once for the missing stat, before any read. A Workflows section with Cancel and progress, on reduce_start and ReduceRun::run(cancel, done), can follow once the parameters are settled.
• minValid is a share, as in zarr.reduce. In cube.trend it is a count. Both meanings were already on main; bringing the two together is left to you.
• Memory by month: a summary by month keeps every month's totals while it reads. That is up to five times the outputs' memory for std, three for the other statistics, and about 640 MB for std at the cap. The code note on MAX_REDUCED and the guide say so. I didn't add a separate byte cap, since it would refuse month climatologies that fit today. A STAC cube's pieces keep cells × dates within MAX_VALUES, which keeps their totals small.
• Order of arrival: only the STAC cube reads several dates at once. Its dates come as they are read, so the groups open at once are those of the dates in flight, and an output's last bit can differ between runs. Stacks, bands and Zarr read one date at a time, in order. Early arrivals aren't held back to force the order: a stalled read would let that buffer grow without bound.

Testing

• a_data_cube_summarised_over_time covers:
  • every statistic over a stack of layers, checked against values worked out by hand (std 1.707825 over six evenly spaced values, for instance);
  • by: "year" and by: "month", with months and a minValid share;
  • a raster whose bands are the dates;
  • a Zarr variable, cell for cell equal to zarr.reduce for mean, std, max and count;
  • a cancelled run;
  • bad requests refused with no layer added: no stat, median, countAbove without above, by: "week", minValid above 1, and a start after the last date.
• a_stac_collection_summarised_over_time, with a local STAC API and range-served COGs as in the STAC trend test: the mean of the whole period and of each month matches each file's own scale and offset, cell by cell, on the full images' grid.
• a_short_cube_is_summarised_but_not_trended: two layers give a mean and a maximum, the trend still refuses them with its own message, and one layer is refused for a summary.
• a_summary_over_a_decreasing_zarr_axis_names_its_period_in_order: a decreasing Zarr axis is refused by the trend and summarised with its period named in order.
• plugin_data_cubes_need_files_and_network: a plugin with edit and files only is refused cube.reduce and cube.trend.
• hostile_params_never_panic gains two sets that give a statistic, so the junk reaches cube.reduce's own keys.
• zarr.reduce's own tests pass unchanged. In a_trend_over_a_stac_collection, a summary read whole, in pieces and by year is compared within 1e-6, since the STAC cube's order of arrival can move the last bit.
• By hand, for a lesson: the 25 annual mean NDVI rasters for Piauí (2001–2025, 1 km, resampling: average) made from the Brazil Data Cube in about 5 minutes.
• cargo fmt --all --check and cargo clippy -p rustgis-engine --all-targets -- -D warnings are clean. The rustgis-engine tests pass on 4555707: 316, 3 ignored.

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📝 Walkthrough

The change adds cube.reduce to summarize selected cube dates by statistic and date grouping. It shares slice-reading and accumulation logic with existing processing, adds tests for local and STAC cubes, and documents the command and its options.

Changes: Temporal Cube Reduction

Layer / File(s)	Summary
Cube requirements and shared slice handling crates/engine/src/cmd/cube.rs	Cube inputs use command-specific date requirements. Shared helpers read slices and validate grids. Trend output pieces use Stitch to check geometry and combined height.
Reduction statistics and grouping crates/engine/src/cmd/cube.rs, crates/engine/src/cmd/zarr.rs	The cube module defines statistics, minValid parsing, grouping, and shared accumulators. zarr.reduce uses the shared statistic and accumulation logic.
Reduction execution and outputs crates/engine/src/cmd/cube.rs	cube.reduce selects dates and groups, accumulates slices, and adds output rasters.
Command integration and validation crates/engine/src/cmd/plugins.rs, crates/engine/src/tests.rs, crates/ui-egui/src/lib.rs, docs/user-guide/analysis.md	Tests cover local and STAC cubes, permissions, and task recording. The user guide describes parameters and outputs.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant reduce_cmd
  participant ReduceRun
  participant read_slices
  participant Totals
  participant add_outputs
  reduce_cmd->>ReduceRun: prepare and run reduction
  ReduceRun->>read_slices: read selected slices
  read_slices-->>ReduceRun: return slice results
  ReduceRun->>Totals: accumulate values and finish groups
  ReduceRun-->>reduce_cmd: return rasters
  reduce_cmd->>add_outputs: add summary rasters

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Possibly related issues

• [Feature]: Trend analysis over a data cube: Sen's slope and the modified Mann–Kendall test, pixel by pixel #579: This change implements cube.reduce summaries across supported cube sources. Sen's slope and Mann–Kendall tests remain separate work.
• Help test RustGIS v0.4.0: new features and existing workflows #748: This change adds tests for summary statistics, grouping, missing values, and parameter validation.

Possibly related PRs

• opengeos/RustGIS#766: Both changes use the top-level STAC input contract for cube commands. This change applies that contract to cube.reduce.

Suggested reviewers: giswqs, jgregoriorincon

Merge Risk: ⚪ Minimal · up to ca3ef

No unresolved issue identified here prevents merging after normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly identifies the main change: adding time-series data-cube summaries grouped by year or month.
Docstring Coverage		Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 28 functions across 4 files. (1 skipped: 1 …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description check		The description includes a detailed Summary and Testing section that explain the changes, scope, validation, and test results. The Related issue section is missing, but this is non-critical because th…

Full details: Docstring Coverage

Explanation

Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 28 functions across 4 files. (1 skipped: 1 too large.)

Full details: Description check

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The description includes a detailed Summary and Testing section that explain the changes, scope, validation, and test results. The Related issue section is missing, but this is non-critical because the rest of the description is complete.

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[github-actions]

Code review

This PR adds cube.reduce, a statistic over time for any time cube, in cube.rs with docs and tests. It also moves shared code out of TrendRun and zarr.reduce: read_slices, off_grid, Stitch, Stat, Totals and min_share. I found no correctness bugs. I read the diff and the changed files, but did not build or run anything.

Bugs

• None found. I checked these, and all look correct:
  • Welford's mean and std accumulation, and the Count and CountAbove paths.
  • The finish thresholds for minValid.
  • The Stitch refactor, which keeps the old piece-stitching checks as they were.
  • The read_slices and off_grid extraction.
  • Group keys, names and per-group date counts.

Security

• None found. Input handling follows the repo's hostile-input rules: get() instead of indexing, checked casts, and a size cap on the outputs. There is no unwrap, expect or panic in the non-test code.

Performance

• Memory (low-medium confidence): all groups' running totals are allocated together. At the 16M-value MAX_REDUCED cap with std, that is about 320 MB on desktop, plus the f32 output bands. See the inline comment.

Quality

• Blocking command (low-medium confidence): reduce_cmd runs blocking, with no cancel and no progress, unlike cube.trend's async path. See the inline comment.
• Nit: in a_data_cube_summarised_over_time, the Zarr temp directory is only cleaned up if the earlier assertions pass. A failure leaks it, which is harmless.
• Positive: the refactor removes duplicated reduction and stitching code, and the tests compare the new path against zarr.reduce cell for cell.

AGENTS.md

• No violations seen. There are no panics, wasm builds are respected (Stat and Totals are ungated, and the zarr re-export keeps its gating), and the changes include docs and tests.
• The command is registered in the engine, so it needs no UI strings.
• I could not run cargo xtask ci or the hostile_params_never_panic test here, so confirm both are green.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 36e8528).

Metric	Value
Files changed	4 (0 added, 4 modified, 0 removed, 0 renamed)
Size before	985.2 KB
Size after	1010.9 KB
Total size change	+25.7 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	60.7 KB	+15.5 KB
crates/engine/src/tests.rs	852.5 KB	864.3 KB	+11.8 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB

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Actionable comments posted: 1

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Inline comments:
Review comments at @crates/engine/src/cmd/cube.rs:
- Line 29: Update the command label in the cube.reduce registration to use
“Summarise” instead of “Summarize,” and update the matching bold command name in
the user guide to the same spelling.

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📖 Docs preview

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[github-actions]

Code review

I read the diff and some surrounding code, but I did not run the tests. The PR adds cube.reduce, a statistic over time for any data cube (all, by year, or by month of the year). It moves the shared pieces out of cube.trend and zarr.reduce into helpers: read_slices, off_grid, Stitch, Stat, Totals. The refactor looks behaviour-preserving, with one exception under Quality. I found no panics or unwrap in non-test code, and the plugin permission and recording registrations are in place.

Bugs

• Order and memory with parallel readers (medium): the comment at cube.rs:1124 says a year-by-year summary holds one year's totals at a time because dates come in order. With several readers, slices arrive out of order. Several groups' totals can then be open at once, which weakens the MAX_REDUCED memory bound. Out-of-order accumulation can also change std, mean and sum in the last bits from run to run. The new tests compare with ==, so they could flake on multi-reader cubes.

Security

• Nothing found. Parameters are validated, sizes are clamped through MAX_REDUCED, and cube.reduce is added to the plugin DATABASES list so plugins need both files and network. A test covers that.

Performance

• Nothing significant. Totals are built per piece and per group. reserve_exact is bounded by MAX_REDUCED.

Quality

• reduce_cmd runs blocking with a throwaway cancel flag and no progress (low to medium). It is unclear whether ReduceRun::total and the cancel/done parameters are wired to the app (see the comment at cube.rs:1269).
• zarr.reduce now skips values equal to the file's no-data value only in cube.reduce. zarr.reduce's loop still checks only is_finite. That seems fine because Zarr has no per-slice nodata here, but it is worth confirming (low).

AGENTS.md

• No violations found. There are no unwrap, expect or panic calls outside tests, Stat is no longer gated on non-wasm, and cube.reduce is registered in the plugin and UI lists. The command's user-visible title ("Summarize a Data Cube over Time") may need an entry in the translation catalogs, but AGENTS.md says the maintainer handles that.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 040e7a8)

Metric	Value
Files changed	6 (0 added, 6 modified, 0 removed, 0 renamed)
Size before	1.17 MB
Size after	1.20 MB
Total size change	+27.9 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	62.1 KB	+17.0 KB
crates/engine/src/tests.rs	852.5 KB	865.0 KB	+12.5 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	−3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B

[github-actions]

Code review

I read the whole diff and the surrounding cube.rs. I couldn't build or run anything, so the tests are unrun and nothing below is confirmed by execution. The refactor of TrendRun into read_slices, off_grid and Stitch looks behaviour-preserving, and I found no definite bugs.

Bugs

• Output size cap not enforced across pieces (low–medium confidence): In ReduceRun::run, when cube.size() is None, only each piece's own cells × outputs is checked. bands keeps growing across pieces, and the running total is never compared with MAX_REDUCED. TrendRun guards this case with too_long. The cap the PR describes therefore only holds for cubes that report their size. I posted an inline comment on this.

Security

• No issues. Input is read with get() and clamped, there are no unwrap/panic calls in the new code, and name is truncated to 200 characters. The plugin permission gate (DATABASES) now includes cube.reduce, and a test covers it.

Performance

• Nothing significant. Slices are folded into running totals, so memory stays bounded. One minor point: keys.iter().filter().count() per group is O(groups × steps), which is negligible at the 20,000-step limit.

Quality

• Shared helpers: Moving the reader, grid check and stitching into shared helpers, and Stat/Totals into one place used by zarr.reduce too, removes duplication. The test checks zarr.reduce against cube.reduce value for value.
• Nit: In ReduceRun::run, stitch.check runs only after all of a piece's slices have been read, so a mismatched piece wastes a full read before the error. TrendRun behaves the same way, so this is just a note.

AGENTS.md

• No unwrap/expect/panic, no unsafe, and std::thread use stays behind cfg(not(wasm32)).
• cube.reduce is a command in cmd/*.rs, as the architecture requires.
• User-visible interface text isn't touched, since there's no dialog.
• Docs are updated in analysis.md.
• I couldn't run cargo xtask ci.

Change size

The whole PR compared with the base branch: the whole PR against main (merge base 4e46ced to PR head b5b2416).

Item	Value
Files changed	6 (0 added, 6 modified, 0 removed, 0 renamed)
Size before	1.17 MB (1,226,157 B)
Size after	1.20 MB (1,254,684 B)
Total size change	+27.9 KB (+28,527 B)

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	62.1 KB	+17.0 KB
crates/engine/src/tests.rs	852.4 KB	864.9 KB	+12.5 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	−3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B

[github-actions]

Code review

I found no blocking problems in PR #774. I read the full diff (cube.rs, zarr.rs, plugins.rs, the tests and the docs) and checked the new code against the surrounding source. I did not run the tests or the build. I posted no inline comments, because nothing met the bar for one.

Bugs

• None found. I traced these paths and they hold:
  • Empty pieces: the case where a piece has no data written is handled. Totals::new(..).finish gives NaN, or 0 for a count when minValid is 0.
  • Group completion: a group's totals are finished when its last date arrives, and unwritten dates still count toward that. Reads in arrival order only change the last bit of an f32 result, which is what the code comment says.
  • Bounds checks: the size cap is checked before reading when the cube knows its size, and per piece when it doesn't. Totals::add and finish use get throughout, so they cannot panic.
  • Count statistics: count and countAbove keep the same "0 where a cell never had a value" behaviour that zarr.reduce had.

Security

• None found. Plugins calling cube.reduce are covered: it is added to the DATABASES list in plugins.rs, which makes it need both files and network. plugin_data_cubes_need_files_and_network tests this for cube.reduce and cube.trend.

Performance

• Memory with by: "month" (low confidence, 0.25). All 12 groups' totals stay open at once, at up to 20 bytes per cell each. The MAX_REDUCED cap is on cells × outputs, so this is bounded, but the peak can be several times the output size on big areas. The doc comment on MAX_REDUCED already says this.

Quality

• Silent fallback to group 0 (low, 0.3). In reduce_start, an unparseable date key falls back to unwrap_or(0) in part and in binary_search(k).unwrap_or(0). The steps come from steps(), which should already have dropped dates that can't be read, so this shouldn't trigger. If it ever did, the date would land in group 0 without any error.
• Refactor: pulling read_slices, off_grid, Stitch, Stat and Totals out of cube.trend and zarr.reduce removes duplicated code. The error message for mismatched slices is unchanged.

AGENTS.md

• Never crash: the new non-test code has no unwrap, expect, panic! or indexing.
• Tests: there are tests for the new command, for cancelling it, for refused parameters, for STAC pieces, and for matching zarr.reduce cell for cell. I did not see cube.reduce added to hostile_params_never_panic. Check that the test covers every registered command automatically, or add it there.
• Interface text: the command spec strings are command metadata, not UI text, so tl! isn't needed.
• Wasm: the cfg(target_arch = "wasm32") handling was moved intact into read_slices. I did not run the wasm build.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 5e1e175)

Metric	Value
Files changed	6 (0 added, 6 modified, 0 removed, 0 renamed)
Size before	1.17 MB
Size after	1.20 MB
Total size change	+28.7 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	63.0 KB	+17.9 KB
crates/engine/src/tests.rs	852.5 KB	865.0 KB	+12.5 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B

[github-actions]

Code review

I read the whole diff and checked the new cube.reduce code against cube_from and the cube.trend and zarr.reduce paths it now shares code with. I found no crashes or correctness bugs in the new code, only the usability and design points below. I did not build the code or run the tests.

Bugs

• Medium confidence: cube.reduce reuses cube_from, which enforces cube.trend's limits. A stack or raster of fewer than 4 layers or bands is refused, so a max or mean over 2–3 dates fails. A Zarr time axis that is descending or repeats a date is also refused, though a plain statistic doesn't need that. Some error text still says "trend", for example a trend takes N dates at most and the wasm messages. (Inline comment on cube.rs.)

Performance

• Medium confidence: reduce_cmd runs the whole summary on the calling thread. A large STAC read could freeze the desktop UI, unlike cube.trend, which has a ran hand-off for background work. ReduceRun::total(), dates() and run(cancel, done) are ready for such a path, but nothing uses them yet. (Inline comment on cube.rs.)

Quality

• The refactor looks behaviour-preserving. read_slices, off_grid, Stitch, Stat, Totals and min_share were pulled out of cube.trend and zarr.reduce with the same logic, and the Zarr path still checks for a different-sized slice. It also removes duplicated code.
• The logic in Totals and ReduceRun::run holds up. Groups that get no data still finish correctly, count returns 0 when no share is asked for, and the cell and output limits are checked before and during reading.
• The new tests cover each statistic, the year and month groupings, minValid, raster bands, Zarr parity with zarr.reduce, cancellation and refused input. Further tests cover STAC reads in pieces and the plugin permission check. The hostile-parameter test also gains two new cases.

Security

• Nothing found. cube.reduce is added to the plugin DATABASES list, so plugins need both files and network permissions, and a test covers that.

AGENTS.md

• No unwrap, expect, panic! or unsafe in the new non-test code; indexing goes through get(). The hostile-parameter test is extended.
• cube.rs has no wasm gating issue. read_slices keeps the cfg(not(wasm32)) threading.
• The command is added to DEFAULTS_TO_ACTIVE_LAYER and the user guide. The command parameter strings are not wrapped in tl!, which is consistent with the other commands.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 8f4fed1).

Metric	Value
Files changed	6 (0 added, 6 modified, 0 removed, 0 renamed)
Size before	1.17 MB (1,226,157 B)
Size after	1.20 MB (1,256,139 B)
Total size change	+29.3 KB (+29,982 B)

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	63.2 KB	+18.1 KB
crates/engine/src/tests.rs	852.5 KB	865.3 KB	+12.8 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B

[github-actions]

Code review

I found no blocking problems. cube.reduce is well structured: the shared read_slices, off_grid and Stitch helpers are extracted cleanly. The Stat and Totals code is moved out of zarr.reduce without changing its parameters or results. I could not run the build or the tests here, so this is a read-through of the diff and the surrounding source.

Bugs

• Minor, low confidence: reduce_start names outputs from steps.first() and steps.last(). cube.reduce now accepts a Zarr time axis that isn't increasing (ordered: false). For a descending axis, names like … 2025–2001 month 03 or a reversed date range could come out backwards. Taking the min and max date over steps would fix it. I left an inline comment on this.
• Cosmetic, low confidence: two steps-count error messages still say "a trend takes … at most" (cube.rs:885, stac.rs:600). They can now be reached by cube.reduce. These lines are not in the diff, so I couldn't comment on them inline. The new Needs::what field could supply the wording.

Security

• None found. Input is handled defensively: get() is used, minValid, months and by are validated, and the output size is capped.

Performance

• Low confidence: the running totals are up to 20 bytes per cell (std), and By::Month holds all 12 groups at once. The MAX_REDUCED cap counts only cells × outputs of f32 output, so a large single-group std run can hold roughly 640 MB of f64 totals. That is far more than the output itself. The code's own comment says pieces bound this, so this only applies when a cube doesn't split into pieces.
• keys.iter().filter().count() for each group is O(groups × steps). That is fine at the 20,000-date limit.

Quality

• The refactor is good: Stat, Totals, min_share and Stat::parse are now shared, with no duplicated parsing left in zarr.rs.
• The new a_data_cube_summarised_over_time test checks cube.reduce against zarr.reduce on the same store.
• hostile_params_never_panic has new junk-parameter cases for the summary.
• plugin_data_cubes_need_files_and_network covers the plugin permissions.

AGENTS.md

• There are no unwrap, expect or panic calls in the non-test code I read.
• The wasm gating looks right: the cfg(wasm32) branches use format! with what.
• cube.reduce is in DATABASES and DEFAULTS_TO_ACTIVE_LAYER.
• No new dependencies or assets.
• The command description is a single top-level key list, as cube.trend has.
• No user-visible UI strings were added.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head ca3ef70).

Metric	Value
Files changed	6 (0 added, 6 modified, 0 removed, 0 renamed)
Size before	1.17 MB
Size after	1.20 MB
Total size change	+31.4 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	63.9 KB	+18.8 KB
crates/engine/src/tests.rs	852.5 KB	866.7 KB	+14.2 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B

[github-actions]

Code review

This PR adds cube.reduce, a statistic over a data cube's time axis, whole-period, by year, or by month. It also pulls the Zarr summary's running totals, the slice-reading loop and the piece stitching into shared helpers that cube.trend and zarr.reduce now use. I read the diff and the changed code. I did not build the crate or run the tests.

Bugs

• No correctness bugs found. I traced these paths:
  • Group totals are opened at a group's first date and finished at its last.
  • A group with no written data in a piece falls back to empty totals at the end of the piece loop.
  • Totals::add returns early for Count, but only after n is incremented, so counts stay right.
  • Unordered Zarr axes work, because names use the earliest and latest date.
  • zarr.reduce behaves as before through the shared Totals.

Security

• Nothing found. Parameters are bounded: names are cut to 200 characters, the cell × output count is capped by MAX_REDUCED, and there is no indexing, unwrap or panic. cube.reduce is added to the plugin permission list (DATABASES in plugins.rs), and a new test covers the files-plus-network requirement.

Performance

• By-month summaries hold up to 12 groups of running totals (up to 20 bytes per cell each) at once. The MAX_REDUCED doc comment says so. Confidence this is acceptable: high.

Quality

• crates/engine/src/cmd/cube.rs:343 (inline comment, low confidence): a layers stack of 1 is accepted for a summary, but a 1-band raster is refused through .max(2). The stack message also reads "needs 1 layers or more". The .max(2) is probably deliberate and deserves a comment.
• Positive: the extraction of Stitch, read_slices, off_grid, Stat::parse and min_share removes duplication without changing behaviour. The new tests cover whole, piece-wise and by-year reads, and the hostile-parameter cases.

AGENTS.md

• No violations found. The new code has no unwrap, expect or panic, nothing in it needs unsafe, and the new code adds no std::time use, so the wasm build path is untouched. The wasm-only errors are handled. The new hostile-parameter cases were added to hostile_params_never_panic.
• I did not check whether the new command's ribbon entry needs its strings wrapped in tl!.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 00b90cc)

Metric	Value
Files changed	7 (0 added, 7 modified, 0 removed, 0 renamed)
Size before	1.22 MB
Size after	1.25 MB
Total size change	+32.4 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	64.2 KB	+19.0 KB
crates/engine/src/tests.rs	852.5 KB	867.4 KB	+14.9 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B
crates/engine/src/cmd/stac.rs	52.3 KB	52.3 KB	+11 B

[github-actions]

Code review

This PR adds cube.reduce, which summarises any time cube with a statistic and can group by all dates, year or month. It also moves Stat and the running totals out of zarr.reduce into cube.rs, and splits read_slices, off_grid and Stitch out of the trend code so both commands share them. I read the whole diff and found no crashes or correctness bugs. I could not build or run anything.

What I checked:

• Never-crash rules: the new code has no unwrap, expect, panic! or indexing, and uses get() and saturating_* throughout.
• Hostile-params test: hostile_params_never_panic gained two cube.reduce cases.
• Empty period: steps() returns an error when no date is left, so the group list can't be empty.
• Wasm: the thread-based reader is still gated for wasm32, and the web-app error messages now use the command's own name.
• Plugin permissions: cube.reduce is added to DATABASES, with a regression test that it needs both files and network.

Bugs

• None found.

Security

• None found.

Performance

• reduce_start counts each group's dates with keys.iter().filter(..).count() for every group (crates/engine/src/cmd/cube.rs, the groups map near the end of reduce_start). That is O(groups × steps) and runs at most about 20,000 dates × a few thousand years. It is not a problem in practice, but a single pass over group_of would be cleaner. Confidence: low. I could not anchor this as an inline comment, so it is listed here.
• With by: "month", the running totals for all 12 groups are held at once, at up to 20 bytes per cell. MAX_REDUCED limits cells × outputs, so the worst case is roughly 320 MB of f64 totals. The doc comment mentions this. Confidence: low, informational.

Quality

• cube.reduce skips values equal to the slice's nodata (inline comment). zarr.reduce, which now uses the same Totals, only skips non-finite values. A Zarr variable with a finite fill value could therefore give different results through the two commands. Confidence: low to medium. The inline comment landed on a line number that may not match the intended line, so check that it is on the right line.
• cube.reduce uses Option<Totals> and finished buffers per piece and group; the logic reads correctly. It is dense, though, and the group-finalisation block would benefit from a short unit test of Totals::finish (minValid and count semantics) in isolation.

AGENTS.md

• No violations found. Plugin permissions are covered, and the docs and tests are updated.
• Nothing is added to ui-egui apart from a small change in lib.rs.
• The PR adds no dependencies.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head b7e206c).

Metric	Value
Files changed	7 (0 added, 7 modified, 0 removed, 0 renamed)
Size before	1.22 MB
Size after	1.25 MB
Total size change	+32.7 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	64.3 KB	+19.1 KB
crates/engine/src/tests.rs	852.5 KB	867.6 KB	+15.1 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B
crates/engine/src/cmd/stac.rs	52.3 KB	52.3 KB	+11 B

[github-actions]

I've posted two inline comments and am now writing the final review summary.

Code review

I found no correctness bugs in the new cube.reduce command or in the refactor that moves the slice reader, grid check and piece stitching out of TrendRun. I read the diff and the surrounding cube.rs and zarr.rs code but did not run the tests.

Bugs

• None found. I checked the group bookkeeping, which holds when dates arrive out of order from several readers. I also checked the cases where a group has no data in a piece, a date has nothing written, and the cube's size is unknown. In each case the output is correct.
• The zarr.reduce refactor onto Stat and Totals keeps its behaviour. It still doesn't skip the file's no-data value, which matches the old code.

Security

• None found. The new code uses get() throughout, clamps sizes with MAX_REDUCED, and has no unwrap, expect or unsafe. The hostile-params test now covers cube.reduce. cube.reduce is in the plugin DATABASES list, so plugins need both files and network permissions.

Performance

• Memory cap ignores totals size (confidence: low–medium, inline comment). MAX_REDUCED caps cells × outputs, but the running totals take up to 20 bytes a cell for every group open at once. With by: "month", all 12 groups stay open until the end of a piece. At the cap that is roughly 640 MB of totals for std, which doesn't fit the "no more memory than a short period" claim.

Quality

• minValid means two things (confidence: medium, inline comment). In cube.reduce it is a share from 0 to 1. In cube.trend it is a count of dates. A distinct key name would avoid mistakes.
• Stale error text (confidence: low). The Zarr ordering error still says "a trend can't be read from it". That is correct today because only the trend sets ordered, but it won't be if another command sets it.

AGENTS.md

• No violations found. The command is in crates/engine/src/cmd/. The wasm paths are guarded and return error messages. The layering is unchanged. Docs and tests were added. No new dependencies or assets.
• Nothing in the diff adds a user-visible string to the egui front end, so tl! doesn't apply.

Change size

Compared with: the whole PR against main (merge base 4e46ced to PR head 36dcaf8).

Metric	Value
Files changed	7 (0 added, 7 modified, 0 removed, 0 renamed)
Size before	1.22 MB
Size after	1.25 MB
Total size change	+32.9 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	64.3 KB	+19.1 KB
crates/engine/src/tests.rs	852.5 KB	867.9 KB	+15.4 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.5 KB	+1.9 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B
crates/engine/src/cmd/stac.rs	52.3 KB	52.3 KB	+11 B

[github-actions]

Code review

I read the whole diff (pr-context/diff.patch) and checked the memory-cap constants against the surrounding source. I did not build or run anything, so the new tests are unexecuted.

PR #774 adds cube.reduce, a summary of a time cube over all dates, by year or by month. It moves Stat, Totals, the slice reader, the grid check and the piece stitching out of TrendRun and zarr.reduce into shared helpers in cube.rs.

Bugs

• No defects found. I traced these paths and they hold up:
  • Totals lifecycle: each group's totals are opened at its first date and finished at its last.
  • Missing data: pieces where a group has no data produce empty or zero outputs as intended.
  • Cancel: it is honoured both inside the readers and after them.
  • Memory cap: MAX_REDUCED = MAX_VALUES / 2 matches the "32 million desktop, 8 million browser" wording in the doc comment.
  • Refactored paths: the trend and Zarr paths keep their behaviour, including the same-grid check.
  • Unordered Zarr axes: the summary allows them, and the trend still rejects them.

Security

• No issues. Plugin permissions are covered: cube.reduce joins the DATABASES list in plugins.rs, and the new test plugin_data_cubes_need_files_and_network covers both commands. The new hostile-parameter cases are added to hostile_params_never_panic.

Performance

• ReduceRun::run keeps a bounded set of running totals, by year or in total, instead of holding the whole block. Output vectors are reserved up front when the cube knows its size.
• Low confidence: by=year over a Zarr axis that is out of order, or read with several readers, can hold more than one year's totals at once. The MAX_REDUCED comment covers the several-readers case but not the out-of-order axis.

Quality

• Low confidence, naming: in reduce_start, the (By::Month, None) layer name omits the {season} suffix that the All and Year names carry. A months filter that narrows the months therefore doesn't show in the name. This is cosmetic. I posted it as an inline comment, but the line number is approximate and it may not attach.
• The refactor (read_slices, off_grid, Stitch, Totals) removes duplication between cube.trend and zarr.reduce, and the helpers are well documented.
• The Zarr time-axis error still says "a trend can't be read from it". It is now reached only when a trend is asked for, so it is correct.

AGENTS.md

• Never crash: I found no unwrap, expect or panics in the new code. Lookups use get(), and the new hostile-parameter tests are added.
• Wasm: the new code is not gated to the desktop. The Zarr and STAC branches return a clear web-app error, and the shared helpers compile for wasm.
• Commands and docs: it is a registered command with a CommandSpec, and the user guide (docs/user-guide/analysis.md) is updated. I saw no new tl! strings, because the command has no UI front end in the diff.

Change size

Compared: the whole PR against main (merge base 4e46ced to PR head 4555707)

Metric	Value
Files changed	7 (0 added, 7 modified, 0 removed, 0 renamed)
Size before	1.22 MB
Size after	1.25 MB
Total size change	+33.4 KB

File	Before	After	Change
crates/engine/src/cmd/cube.rs	45.1 KB	64.6 KB	+19.5 KB
crates/engine/src/tests.rs	852.5 KB	867.9 KB	+15.4 KB
crates/engine/src/cmd/zarr.rs	54.0 KB	50.4 KB	-3.6 KB
docs/user-guide/analysis.md	33.6 KB	35.8 KB	+2.1 KB
crates/engine/src/cmd/plugins.rs	28.6 KB	28.6 KB	+19 B
crates/ui-egui/src/lib.rs	183.6 KB	183.6 KB	+19 B
crates/engine/src/cmd/stac.rs	52.3 KB	52.3 KB	+11 B