feat(local): aggregate blocked-on-dependency reporting by dependency (#131)

## Why

With cascade detection (#128) live, the latest `auto-apply-patches` run did exactly the right thing — **proposed nothing** (`No auto-proposable candidates`) because every failure is a dependency cascade, and it surfaced the ~30 root-cause dependencies to fix.

But the "Blocked on a dependency" list printed **one line per fingerprint group**, so the same dependency repeated (rstan ×4, lpsymphony ×4, salso ×2, BH ×2, GO.db ×2, RcppCWB ×2, …), burying the priority.

## What

Aggregate blocked packages across all groups **by the dependency they wait on**:

- Expose `blocked_map` (package → dependency) from `build_triage_report()`.
- Add `blocked_by_dependency()` — dedupes dependents (a package in two groups counts once) and ranks dependencies by how many distinct dependents they block.
- Proposer and tracker (log + issue) now print one line per dependency, sorted by impact. Replaces the per-group `blocked_summary`.

## Result (same data, aggregated)

```
Blocked on a dependency (3 dependencies block 6 dependents; fix the dependency, not each dependent):
  RcppParallel             3 dependent(s)
  rstan                    2 dependent(s)
  sf                       1 dependent(s)
```

So the real run becomes a crisp, ranked worklist: RcppParallel (894), sf (128), rstan (~96), Rfast (33), clarabel/DescTools (26), Rglpk (22), xgboost (18), …

## Verified

New test covers cross-group aggregation, dedup (a dependent in two groups counted once), the example cap, and ranking. 112 tests pass; hooks pass.

Reviewed-on: #131

local/failing-builds-classify.R

@@ -385,6 +385,7 @@ build_triage_report <- function(
       applies_to = sig$applies_to,
       blocked_on = blocked_on,
       blocked_packages = blocked_packages,
+      blocked_map = if (length(blocked_map) > 0L) blocked_map else NULL,
       fingerprint = names(fp_tab)[[1L]],
       fingerprint_variants = length(fp_tab),
       build_count = nrow(g),

local/proposal-tracking-lib.R

@@ -160,24 +160,38 @@ unclassified_summary <- function(report, max_groups = 30L, max_pkgs = 15L) {
   )
 }
 
-# Groups with packages blocked on a dependency (a package-specific fix pinned
-# via `applies_to`, or a data-driven cascade where the package fails building a
-# dependency): report the dependency + how many dependents wait on it, so fixing
-# it once is recognised as clearing the batch.
-blocked_summary <- function(report, max_pkgs = 15L) {
-  bl <- Filter(
-    function(g) length(g$blocked_packages %||% character(0L)) > 0L,
-    report
-  )
-  lapply(bl, function(g) {
-    pkgs <- g$blocked_packages
+# Aggregate blocked packages across ALL groups by the dependency they wait on,
+# so one dependency (RcppParallel, rstan, sf, ...) is a single line -- deduped
+# and ranked by how many distinct dependents it blocks -- instead of repeating
+# once per fingerprint group. Reads each group's `blocked_map` (package -> the
+# dependency it is blocked on). Returns records sorted by dependent count desc,
+# each with up to `max_pkgs` example dependents.
+blocked_by_dependency <- function(report, max_pkgs = 15L) {
+  acc <- list() # dependency -> character vector of dependent packages
+  for (g in report) {
+    bm <- g$blocked_map
+    if (is.null(bm) || length(bm) == 0L) {
+      next
+    }
+    for (pkg in names(bm)) {
+      for (dep in as.character(unlist(bm[[pkg]]))) {
+        acc[[dep]] <- unique(c(acc[[dep]], pkg))
+      }
+    }
+  }
+  if (length(acc) == 0L) {
+    return(list())
+  }
+  out <- lapply(names(acc), function(dep) {
+    pkgs <- acc[[dep]]
     list(
-      blocked_on = g$blocked_on,
+      dependency = dep,
       n_packages = length(pkgs),
       packages = utils::head(pkgs, max_pkgs),
       packages_truncated = length(pkgs) > max_pkgs
     )
   })
+  out[order(-vapply(out, function(x) x$n_packages, integer(1L)))]
 }
 
 # Does a registry entry's `platforms` apply to a build on `os` (e.g.

local/proposal-tracking.R

@@ -127,13 +127,13 @@ if (length(retire) > 0L) {
 # ---------------------------------------------------------------------------
 # Blind spots: failures the classifier could not auto-propose.
 # ---------------------------------------------------------------------------
-blocked <- blocked_summary(report)
+blocked <- blocked_by_dependency(report)
 unmatched <- unclassified_summary(report)
 
 cat("\nBlocked on a dependency (fix the dependency, not each dependent):\n")
 if (length(blocked) > 0L) {
   for (b in blocked) {
-    cat(sprintf("  %s: %d dependent(s) waiting\n", b$blocked_on, b$n_packages))
+    cat(sprintf("  %-20s %5d dependent(s)\n", b$dependency, b$n_packages))
   }
 } else {
   cat("  (none)\n")
@@ -207,8 +207,8 @@ if (do_issue) {
       body_lines <- c(
         body_lines,
         sprintf(
-          "- **%s**: %d dependent(s) waiting (e.g. %s%s)",
-          b$blocked_on,
+          "- **%s**: %d dependent(s) (e.g. %s%s)",
+          b$dependency,
           b$n_packages,
           toString(b$packages),
           if (isTRUE(b$packages_truncated)) ", ..." else ""

local/propose-patches.R

@@ -148,21 +148,20 @@ for (r in report) {
   }
 }
 
-# Groups blocked on a dependency (e.g. RcppParallel dependents) are reported,
-# not proposed: fixing the named dependency clears them all at once.
-blocked <- Filter(
-  function(r) length(r$blocked_packages) > 0L,
-  report
-)
+# Packages blocked on a dependency are reported (aggregated by dependency,
+# ranked by impact), not proposed: fixing the named dependency clears the batch.
+blocked <- blocked_by_dependency(report)
 if (length(blocked) > 0L) {
-  cat("\nBlocked on a dependency (fix the dependency, not each dependent):\n")
-  for (r in blocked) {
+  n_blocked_pkgs <- length(unique(unlist(
+    lapply(report, function(r) r$blocked_packages)
+  )))
   cat(sprintf(
-      "  %s: %d package(s) fail because %s does not build\n",
-      toString(r$blocked_on),
-      length(r$blocked_packages),
-      toString(r$blocked_on)
+    "\nBlocked on a dependency (%d dependencies block %d dependents; fix the dependency, not each dependent):\n",
+    length(blocked),
+    n_blocked_pkgs
   ))
+  for (b in blocked) {
+    cat(sprintf("  %-20s %5d dependent(s)\n", b$dependency, b$n_packages))
   }
 }
 

local/tests/test-proposal-tracking-lib.R

@@ -146,20 +146,35 @@ test_that("unclassified_summary ranks unknown groups and caps output", {
   expect_identical(capped$dropped_groups, 1L)
 })
 
-test_that("blocked_summary lists each dependency and its dependent count", {
+test_that("blocked_by_dependency aggregates across groups, deduped and ranked", {
+  # RcppParallel dependents split across platforms/fingerprints -> separate
+  # groups, but one aggregated line; a dependent seen twice is counted once.
   failures <- data.frame(
-    name = c("ACEsimFit", "AovBay", "AdaptGauss"),
-    platform = "ubuntu-2604",
+    name = c("ACEsimFit", "AovBay", "AdaptGauss", "ACEsimFit", "loner"),
+    platform = c(
+      "ubuntu-2604",
+      "ubuntu-2604",
+      "alpine-324",
+      "alpine-324",
+      "ubuntu-2604"
+    ),
     arch = "amd64",
-    error_text = "Error: USE_TBB=Linux is not supported on this toolchain",
+    error_text = c(
+      rep("Error: USE_TBB=Linux is not supported on this toolchain", 4L),
+      "Failed to build source package rstan.\nfatal error: tbb/tbb_stddef.h"
+    ),
     stringsAsFactors = FALSE
   )
   report <- build_triage_report(failures, registered_pkgs = character(0L))
-  b <- blocked_summary(report, max_pkgs = 2L)
-  expect_length(b, 1L)
-  expect_identical(b[[1L]]$blocked_on, "RcppParallel")
-  expect_identical(b[[1L]]$n_packages, 3L)
-  expect_true(b[[1L]]$packages_truncated)
+  agg <- blocked_by_dependency(report, max_pkgs = 2L)
+  deps <- vapply(agg, function(b) b$dependency, character(1L))
+  expect_true("RcppParallel" %in% deps && "rstan" %in% deps)
+  rcpp <- Filter(function(b) b$dependency == "RcppParallel", agg)[[1L]]
+  # ACEsimFit appears in two groups -> counted once (3 distinct dependents).
+  expect_identical(rcpp$n_packages, 3L)
+  expect_true(rcpp$packages_truncated) # capped at max_pkgs = 2
+  # Ranked by dependent count: RcppParallel (3) before rstan (1).
+  expect_identical(deps[[1L]], "RcppParallel")
 })
 
 test_that("entry_applies_to_os matches codename, family, and wildcard", {