cd_summary(): tell apart stations sharing a long_name and mixed-scale trends

[NewGraphEnvironment]

Summary

cd_summary() keeps every row distinguishable (#98).

• Stations sharing a long_name. A long_name carried by several variables gets the variable appended: Mean discharge (q_site1), Mean discharge (q_site2). The rule is the one cd_plot_comparison() has used since cd_plot_timeseries() and cd_plot_comparison(): use long_name/unit carried on the input #93, lifted into one internal helper, label_disambiguate() in R/cd_anomaly.R, which both call. Registered ERA5 variables are unaffected, because registry long_names are unique (pinned by a test).
• Raw-value and anomaly trends in one table. bind_rows(cd_trend(x), cd_trend(ano)) gave rows differing by Unit at most, and for tmean not even that. When a table holds both scales, a Trend on column (Value/Anomaly) now follows Period. It uses the same rule as Unit: only trend_on == "value" is a raw-value trend, and a missing or NA value reads as Anomaly. A table on one scale keeps its shape, so both vignettes' tables are unchanged.

Behaviour changes for existing callers:

• cd_summary() Parameter gains (variable) wherever several variables share a label.
• cd_summary() gains a Trend on column only when the input mixes scales.
• cd_plot_comparison() in the contrived case where a suffixed label meets another variable's own label (long_name = c("Q", "Q", "Q (a)")): the facets now read Q (a) (a), Q (b), Q (a) (c) instead of Q (a), Q (b), Q (a). Each variable already had its own facet, and now each also has its own label.
• A variable name built to collide (a) (a beside a) gives labels that never settle, so cd_summary() and cd_plot_comparison() abort ("Rename the variables…") rather than print two variables under one name. cd_plot_comparison() plotted that input on main.

Review

Records are in planning/archive/2026-09-issue-98-summary-station-labels/.

• Plan review: no blockers. It found a third source of look-alike rows, several trend_start values, now filed as cd_summary(): trends from several trend_start values differ only by Years #106.
• /code-check, three rounds over the whole branch. The helper's repeat loop was twice bounded by reasoning, and wrong both times:
  • Round 1: the bound (number of variables) was too small when one variable carries different labels by period.
  • Round 2: a variable name built to collide (a) (a) never settles, so the helper aborts. That abort is now pinned by a test.
  • Round 3: narrowed an overclaim about which functions call the helper. cd_plot_timeseries() plots one variable and does not.
  • The loop ended by enumeration, not a reviewer's say-so. Every set of 1-4 (variable, label) pairs over a small alphabet, 66,711 sets, gave 0 aborts and 0 labels shared by two variables.
• Mutation check: removing the station fix, the Trend on block, or the helper's abort each turns the new tests red.

Test plan

• devtools::test(): 395 pass, 0 fail. The 6 warnings are the existing row-names warning in cd_plot_comparison().
• devtools::document() regenerated cd_summary.Rd, cd_plot_comparison.Rd and cd_plot_timeseries.Rd.
• pkgdown::check_pkgdown() fails on main already (DESCRIPTION URL lacks the github.io address). This branch adds no export.

Notes

• Found while opening this PR and filed separately as .Rbuildignore misses planning/, scripts/, data-raw/, logs/, dev/, .claude/, CLAUDE.md - all ship in the tarball #107: .Rbuildignore misses planning/, scripts/, data-raw/ and more, so they ship in the tarball.
• NEWS and the version bump (0.5.4) are left to /gh-pr-merge.

Fixes #98

Relates to NewGraphEnvironment/sred-2025-2026#23

🤖 Generated with Claude Code

https://claude.ai/code/session_01GignjoKpZADXywTf6pAMgj