fix(explore): guarantee an agent-named symbol renders, wherever it sits (CG-38)

`codegraph_explore` never returned `queueMessage` (L1087) or
`flushQueuedMessages` (L1102) from a 1,414-line file, on a symbol bag or a
prose question, even with that file at rank #1 holding 67% of the envelope —
the agent got a same-stem `QueuedMessage` interface at L70 and had to Read the
file for the functions it had named. Pre-existing at every build including
pre-epic (controlled bisect, index held fixed).

Two independent causes:

1. `buildFlowFromNamedSymbols` returns the Flow prose AND the set of node ids
   the agent named — and the latter is the whole guarantee, since it injects a
   named def into its file's cluster ranges at importance 9. Its bail-outs
   returned EMPTY, zeroing the identity whenever there was nothing to PRINT.
   Two sibling closures that never call each other produce no chain, no synth
   hop and no boundary, so both defs lost importance 9 and the file rendered
   from its head. `identityOnly()` now separates the two, gated on
   shape-precise tokens so a prose word that exact-matches a callable cannot
   promote itself.

2. The ceiling trim filled in SOURCE order, so an over-ceiling render always
   dropped the END of a large file first. The shrink HAD kept both symbols
   (1022-1121); the trim cut back to 839. `windowToCeiling` now takes the
   spine call site plus every importance>=9 member as focus lines, tries the
   full ceiling first, and splits the held-back reserve evenly with
   carry-forward — greedy-in-source-order reproduced the bug one level down.

The shrink's loose size estimate is left alone deliberately, and the comment
now says why: making it exact was built and measured WORSE (it stops at the
last member that fits whole and the released bytes carry forward to
lower-ranked files, costing payroll-go's `s.store.Upsert`). `bound()` clamps to
the ceiling anyway, so the slack costs no bytes; it just must not pick the
survivors, which is what the trim now handles.

The measurement gap this closes: every existing probe is aggregate — envelope
share, per-file spend, source totals, file counts — and all are green on a
response that returns 25K from the right file and omits the named function.
`probe-named-symbol.mjs` checks the definition LINE against the response's
rendered lines, per symbol.

Suite envelope byte-identical to main on all six repos; probe-allocation 4/4,
no starvation flags; 180 files / 2,997 tests green. Fixture: 7/7 fail on main,
7/7 pass here, deterministic over 4 runs per arm.

CHANGELOG.md

@@ -35,6 +35,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Every file `codegraph_explore` decides to include now actually arrives. A file shown in full could still spend room set aside for files below it — the fix above covered files shown as excerpts but not files shown whole — and the answer's own size bookkeeping under-counted each file's heading, so the answer ran past its limit and a fully prepared file was discarded at the end. A file that no longer fits whole is now shown as excerpts instead of vanishing, and one that overshoots by a little is trimmed to fit rather than dropped.
 - The list of files an answer could not cover — the "explore these names for their source" pointers — is no longer thrown away when the answer is full. It is now budgeted for and trimmed to fit, so a full answer still tells you what it left out and which names to ask for next, instead of ending with no pointers at all.
 - When a `codegraph_explore` answer shows a file as excerpts, a large excerpt that no longer fit was dropped entirely instead of being shortened. If the file's first excerpt happened to be a trivial one — an import block, a one-line helper next to the code you asked about — the excerpt carrying the actual answer was the one thrown away, and the file came back with a quarter of the room it had been given. On real projects that meant the top-ranked file delivered a fraction of its share while a far less relevant file took the rest. Excerpts are now shortened to fit, whole method by whole method, and only dropped when what is left is too small to hold anything readable.
+- When you name a symbol in a `codegraph_explore` query, its definition now actually comes back. Two cases previously lost it. If the symbols you named don't call one another — sibling functions inside the same factory or module are the everyday example — CodeGraph stopped treating them as symbols you had asked for, and answered with whatever sat at the top of their file instead; on one 1,400-line file that meant a same-stem `QueuedMessage` interface on line 70 came back while the `queueMessage` function on line 1087 did not. And when an answer had to be trimmed to fit, it was trimmed from the bottom of the file down, so a symbol near the end of a long file was always the first thing cut. Trimming now protects the definitions you named wherever they sit in the file.
 - The blast-radius section of `codegraph_explore` flagged "no covering tests found" whenever no test called a symbol directly — falsely branding helpers that tests exercise through their callers as untested (about 40% of flagged symbols in a measured sample). The check now follows caller chains up to 3 hops and reports indirect coverage as "tested via callers"; when nothing is found it states exactly what was checked instead of an unconditional warning. Thanks @inth3shadows for measuring the false-positive rate. (#1475)
 
 ## [1.5.0] - 2026-07-21